DIY GUIDE · PLUMBING & HEATING

How to replace a basin waste and bottle trap yourself
A couple of hours. £21–£47 for a new waste, a trap and sealant.

Slow drain, smell, drip or a dead pop-up plug. Clear it, then swap the waste and trap — the pipes stay where they are.

DIFFICULTY
Easy
part of the job only
TIME
One to three hours
most of it getting the old waste out of the basin and the sealant off
MATERIALS
£21–£47
a click-clack or pop-up basin waste, a bottle trap and a tube of sanitary silicone
A PRO CHARGES
£150–£2,200
typically £900
  • Every step, start to finish
  • Checked October 2026 — sources at the end
  • Honest about when to call a pro

FIRST, THE HONEST ANSWER

Do it yourself, or get a plumber?

Do it yourself if…

  • The basin drains slowly, smells, or drips at the trap or the plug fitting
  • The pop-up or click-clack plug is broken, stuck or will not seal
  • You are fitting the same type of waste and trap to the same basin and the same waste pipe
  • You can reach under the basin, or the pedestal or vanity panel comes away

Get a pro if…

  • The waste pipe behind the trap is cracked, sagging, or leaks inside the wall
  • The basin is moving, a new basin is going in, or the waste has to be rerouted
  • Water runs back into the basin from other appliances, or several fittings are slow at once
  • The basin itself is cracked, or the taps or their supply pipes need work at the same time

Safety first

  • Put on rubber gloves before you open a trap. It holds standing waste water, hair and soap scum, and it smells.
  • Never open a trap after pouring in a chemical drain unblocker. HSE's guidance on hazardous substances is about knowing what a product does to skin and eyes; these products are strong acids or alkalis, and the trap will be full of them.
  • Wear safety glasses when working under a basin. Grit and old water fall straight towards your face.
  • Ceramic basins crack if a back nut is forced. Tighten plastic nuts by hand, and only a little more on chrome.
  • If there is a shaver socket, light or heater near the basin, switch it off before water can reach it.

Stop here: Stop here: new bathroom plumbing, the drains and the electrics

Replacing a basin's waste and trap like for like is maintenance. In England, a new bathroom, or one where plumbing is added or altered, is notifiable building work unless a registered installer does it, and new drainage falls under Part H; Wales, Scotland and Northern Ireland have their own building regulations covering the same ground. Anything on the supply side is a water fitting and must meet the 1999 Water Fittings Regulations in England and Wales, the Scottish Water byelaws in Scotland or Northern Ireland's 2009 Water Fittings Regulations, and installing a bath over 230 litres or a bidet with a flexible hose needs notice to the water supplier first. Bathrooms are special locations for electrics: new circuits or alterations near a bath or shower are notifiable in England under Part P, and Wales, Scotland and Northern Ireland apply their own rules. How to hire a bathroom plumber →

MATERIALCOVERAGEFOR THIS JOB
Basin wasteSlotted if the basin has an overflow, unslotted if notOne, with its washers
Bottle trapMatched to the waste size, with a deep water sealOne
Sanitary siliconeLow-modulus, mould-resistant, only if the waste's instructions call for itOne small tube
Silicone greaseFor trap O-rings, if the trap's instructions ask for itA smear

Will the trap line up with the pipe

Trap height needed = height of the waste tail outlet above the floor − height of the pipe centre in the wall. If the waste tail ends 650 mm up and the pipe centre is 520 mm up, the trap must drop 130 mm; an adjustable bottle trap with that range fits without cutting.

The trap's own instructions set a small fall back towards the wall so water runs away; one we checked gives about five degrees.

Slotted or unslotted waste

Look in the bowl for an overflow: a slot or holes near the rim. A basin with an overflow needs a slotted waste, which has a gap in its side that lines up with the overflow channel. A basin without one needs an unslotted waste. Fitting an unslotted waste to a basin with an overflow blocks the channel; the overflow then does nothing and stale water sits in it.

Click-clack, pop-up or plug and chain

A click-clack waste opens and shuts when you press the plug. A pop-up waste works from a lever behind the tap, through a rod under the basin. A plug and chain is the simplest and the hardest to break. A pop-up uses the tap's rod hole; if your new tap has no rod, you need a click-clack or a plug and chain.

Bottle trap or tubular trap

A bottle trap is compact and its bottom unscrews for cleaning, which makes it the usual choice under a basin. A tubular trap is a P or S shaped bend, which flows better but takes more room. Most bathroom basins use the common small waste size; check the outlet of your waste and the pipe in the wall. Choose one with a deep water seal; a shallow seal can be siphoned dry and lets smells through.

Adjustable inlet

Many bottle traps have an adjustable inlet that slides up and down the waste tail. That lets the trap outlet line up with the pipe in the wall without cutting anything. If your old trap was a fixed height and the pipe sat awkwardly, an adjustable one fixes it.

Washers and sealant

A basin waste seals to the bowl with rubber washers above and below, and some makers ask for a bed of sanitary silicone as well. Read the waste's own instructions. Buy a small tube of low-modulus sanitary silicone if they call for it; general-purpose sealant goes mouldy in a bathroom.

Measure the thickness of the basin at the plughole; some wastes are too short for thick ceramic.
Take the old waste to the shop if you can; the slot and the thread size are easiest matched by eye.

THE PART THAT DECIDES THE FINISH

Before you start — what is under your basin

What you can reach decides how easy this is. Look under the basin with a torch and match it to one of these.

Open basin on a wall or pedestal

The trap and waste are in view, or behind a loose pedestal.

  1. If there is a pedestal, check whether it is screwed to the floor or just sits there; lift it away gently
  2. Put a bowl under the trap and a towel on the floor
  3. Photograph the trap, the waste pipe and any pop-up rod linkage
  4. Check the basin is firmly fixed to the wall before you lean on it
Vanity unit or cabinet

The trap is inside a cupboard, often with little room.

  1. Empty the cupboard and take out any removable back panel
  2. A head torch frees both hands
  3. Check whether the basin is sealed down to the unit with silicone; the waste may need to be reached from above as well
  4. Protect the cupboard base with a towel; chipboard swells as soon as it gets wet
Slow drain, no leak

The usual reason to start this job.

  1. Clear the plug fitting first: lift out a click-clack plug or unhook a pop-up rod and pull the plug
  2. Pull hair out with a plastic drain hook rather than a wire coat hanger, which scratches the waste
  3. Unscrew the bottom of the bottle trap into a bowl and clean it
  4. Run water hard for a minute; if it still backs up, the blockage is in the pipe beyond the trap
Drip under the basin

A leak, which tells you which part to replace.

  1. Dry everything and fill the basin, then pull the plug and watch with a torch
  2. A drip from the waste's back nut means the waste washer or seal
  3. A drip from the trap joints means a trap washer or a loose nut
  4. A drip from the wall end of the trap means the pipe connector or the pipe itself

THE JOB

How to replace the waste and trap

  1. Set up: clear the space and empty the basin

    15 min

    Find your case in the cards above. Empty the cupboard or move the pedestal, lay towels, and put a bowl under the trap. Put on gloves and glasses. Photograph the trap, waste and any pop-up rod from two angles.

    • Turn off any shaver light or socket above the basin
    • Put the plug in the bath so small parts cannot go down it
    • Stand the new parts in their bags on the closed toilet lid where you can reach them

    Mistake to avoid: Starting with the basin full of water or straight after using a drain chemical. The trap then empties chemical-laden water over your hands.

  2. Clear it first

    20 min

    This is the slow-drain card above, and it may be all you need. Lift out the plug, pull out hair with a plastic hook, then unscrew the bottom of the bottle trap into the bowl and clean it and the inside of the trap body with an old brush. Refit the bottom hand tight and run the tap hard. If it now drains well and does not drip, the job is done.

    • On a pop-up waste, loosen the rod linkage under the basin to lift the plug out
    • Check the bottle trap's O-ring or washer while it is apart; a flattened one drips
    • Do not use a wire hanger; it scratches the waste and hooks the hair further in

    Mistake to avoid: Replacing a waste that only needed cleaning. A clogged pop-up mechanism is usually hair round the plug stem, not a broken part.

  3. Remove the trap

    10 min

    Undo the nut that holds the trap to the waste tail, then the nut at the wall end, by hand. Lift the trap away and tip it into the bowl. Stuff a rag loosely in the open pipe at the wall so drain smells and gases stay in the pipe while you work.

    • Plastic nuts loosen anticlockwise as you look down on them
    • If a nut is stuck, wrap it in a cloth and use grips gently; plastic cracks
    • Keep the old trap until the new one is in and dry

    Mistake to avoid: Forgetting the rag in the pipe and then pushing the new trap onto it. Remove it before you fit the new trap.

  4. Remove the old waste

    30 min

    Under the basin, undo the large back nut on the waste tail, using a basin wrench if it is metal and stuck. With the nut off, push the waste up and out of the bowl from below. Scrape every trace of old sealant and limescale from around the plughole with a plastic scraper and a blade held flat, then clean with washing-up liquid and dry.

    • A stubborn waste may be bedded in old putty or sealant; tap it upwards from below with the heel of your hand
    • Disconnect the pop-up rod from the waste before you pull it
    • Clean the overflow channel with a bottle brush while you have access

    Mistake to avoid: Prising the waste out from above with a screwdriver. It slips and chips the basin's glaze round the plughole.

  5. Fit the new waste

    20 min

    Follow the waste's own instructions for washers and sealant. On a slotted waste, line the slot up with the overflow channel. Put the top washer or a bead of silicone under the flange, push the waste down through the hole, and from below fit the bottom washer and the back nut. Tighten the nut by hand, firmly, while someone holds the flange straight from above; on ceramic, go no further than hand tight plus a small nip.

    • Wipe away squeezed-out silicone with a damp finger before it skins
    • Check the slot faces the overflow before the nut is tight
    • If the waste spins as you tighten, hold the grate with the handles of pliers inside it

    Mistake to avoid: Over-tightening the back nut on a ceramic basin. The basin cracks round the waste, and that is a new basin.

  6. Fit the new trap

    20 min

    Slide the adjustable inlet or the top nut and washer over the waste tail. Offer the trap up so its outlet lines up with the pipe in the wall, with a gentle fall back towards the wall, and tighten the top nut by hand. Fit the wall end, either onto the pipe directly or through the connector, and tighten that nut by hand. Wipe trap O-rings with silicone grease first if the instructions ask.

    • Hand tight on plastic is enough; the washers do the sealing
    • A trap pulled into place under strain will leak; adjust the inlet height instead
    • Make sure the cleaning cap at the bottom is screwed fully home

    Mistake to avoid: Using PTFE tape or sealant on plastic trap threads. The washers then do not seat, and the joint weeps.

  7. Reconnect a pop-up rod

    15 min

    On a pop-up waste, feed the lift rod down through the tap, connect it to the waste's lever or linkage as its instructions show, and adjust it so the plug opens fully and seals fully. Work it several times while watching from below.

    • Adjust with the plug in place; the stop setting is easy to get slightly wrong
    • A plug that will not close fully usually needs the clevis moved one hole
    • Check the rod does not foul the trap or the wall

    Mistake to avoid: Setting the rod so the plug only half opens. The basin drains slowly, and it looks as though the new waste has failed.

  8. Test with a full basin

    15 min

    Let any silicone skin over as its tube says. Fill the basin to the overflow and leave it for a few minutes, then pull the plug. Watch every joint with a torch and a dry tissue as the water rushes through. Run the tap into the overflow too, to check the slot lines up.

    • A tissue under each joint shows a weep long before you see a drip
    • A joint that weeps usually needs a quarter turn more by hand
    • Leave a sheet of kitchen roll in the cupboard or behind the pedestal overnight

    Mistake to avoid: Testing with a trickle from the tap. A trickle never fills the trap or pressurises the joints, and the leak only shows the first time someone empties a full basin.

The mistakes that show

  • Fitting an unslotted waste to a basin with an overflow
  • Over-tightening a back nut on a ceramic basin
  • Taping or sealing plastic trap threads instead of trusting the washers
  • Pulling a trap into line under strain instead of adjusting it
  • Opening a trap full of chemical drain cleaner

Stop here and get a plumber

  • The waste pipe behind the trap is cracked, sagging or leaking inside the wall
  • The basin is being moved, or a new basin needs new waste or supply pipework
  • Several fittings drain slowly or water backs up from one into another
  • The basin is cracked, or its taps or supply pipes need work too
How to hire a bathroom plumber →

Basin draining slowly after the new wasteThe pop-up rod is not opening the plug fully, or the trap is pulled up into a hump. Adjust the rod so the plug lifts all the way and reset the trap height.
Bad smell from the plugholeThe trap seal is being siphoned dry, or the overflow channel is fouled. Fill the basin and drain it to refill the trap; clean the overflow with a bottle brush; fit a trap with a deeper seal if it keeps happening.
Drip from under the waste back nutThe bottom washer is not seated or the nut is short of tight. Hand-tighten a little more; if it still drips, take it apart and reseat the washer.
Water coming out round the plug flangeThe top seal or silicone bed has a gap. Remove the waste, clean off and refit with a fresh bead.
Click-clack plug will not stay downThe spring mechanism has hair or scale in it. Unscrew the plug, clean the stem and spring, and refit; if the spring is broken, a replacement plug is sold for most wastes.
Gurgling as the basin emptiesThe trap is being siphoned by the long pipe run. A resealing or anti-siphon trap fixes it.
Trap leaks at the wall endThe pipe end is not pushed into the connector far enough or is cut at an angle. Remove the trap, check the pipe end is square, and refit.
Water appears from the overflow when the plug is inAn unslotted waste was fitted to a basin with an overflow, or the slot does not line up. Turn the waste so the slot faces the overflow, or replace it with a slotted one.

WHAT YOU SAVE

What it costs to do it yourself

Basin waste, click-clack or sprung£9–£25
Bottle trap£4–£12
Sanitary silicone£8–£10
Total£21–£47
DIY total£21–£47
A bathroom plumber charges per job
LOW
£150
TYPICAL
£900
HIGH
£2,200
Bathroom Plumbing price guide →

Guide prices compiled by the Locufy team from published Irish and UK provider price lists and 2026/27 cost guides. Updated 2026.

A plumber's guide price for bathroom plumbing covers far bigger jobs; this is a parts-only job you can do in an afternoon, and most of the time cleaning the trap fixes it for nothing.

RATHER NOT?

Bathroom plumbers near you, with prices shown

The ones who cover your area, nearest first, with one score from every review. No account needed to look.

Or post the job free and let them come to you.

Let the sealant cure

Leave silicone untouched for the time on its tube before running a basin full; touch-dry is not cured.

Clean the trap every few months

Unscrew the bottom of the bottle trap into a bowl and rinse it. Hair and soap build up gradually and slow the basin long before it blocks.

Dispose of the old parts

Plastic traps and wastes go in general waste. Chrome or brass wastes go to the metals container at your council's household waste recycling centre. Never pour chemical unblockers or old sealant down the drain; take leftover chemicals to the household hazardous waste point at the same centre. Find yours on the council website or the recycling pages for your nation.

Keep a drain hook

A plastic hook in the bathroom cabinet clears a click-clack waste in a minute and saves a chemical.

Replacing a basin waste and bottle trap: questions people ask

The trap's water seal has dried out or been siphoned, or the overflow channel is fouled with soap and hair. Run the basin full and drain it, clean the overflow, and clean the trap. If it keeps happening, fit a resealing trap.

Lift out the plug and pull hair out with a plastic hook, then unscrew the bottom of the bottle trap into a bowl and clean it. That clears most basins. Chemicals are a last resort and make taking the trap apart dangerous.

Slotted if the basin has an overflow hole or slot near the rim, unslotted if it does not. The slot lets the overflow drain through the waste.

Follow the waste's instructions. Many use rubber washers only; some ask for a bed of sanitary silicone under the flange. Use a mould-resistant sanitary grade if you do.

Hand tight. The washers make the seal, and grips or a spanner crack the nuts. A weep usually needs a quarter turn more by hand, not tools.

Locufy's UK price guide puts bathroom plumbing at £150–£2,200 per job, typically £900 — the same three figures as the strip at the top of this page. Those jobs are mostly far bigger than a waste and trap.

MORE GUIDES

More DIY guides

Unblocking a sink, bath, toilet or outside drainReplacing a kitchen mixer tap like for likeResealing a bath, shower or sinkFixing a running or slow-filling toiletReplacing a shower head, hose and riser railDoing the small plumbing jobsHandling a plumbing emergency until help arrivesBleeding radiators and re-pressurising
All 90 DIY guides →How to hire a bathroom plumber →Bathroom Plumbing price guide →Bathroom plumbers on Locufy →

Sources — checked October 2026

  1. Flat-bottom basin bottle trap installation instructions — fitting order, fall to the wall, cleaning access
  2. HSE — COSHH basics: hazardous substances
  3. HSE — manual handling at work
  4. Water Supply (Water Fittings) Regulations 1999, regulation 5 — notice for baths over 230 litres and bidets
  5. Water Supply (Water Fittings) (Scotland) Byelaws Extension Order 2024
  6. Water Supply (Water Fittings) Regulations (Northern Ireland) 2009
  7. gov.uk — building work, replacements and repairs to your home (England)
  8. gov.uk — Approved Document P: electrical safety in dwellings (England)
  9. gov.uk — recycling collections: find your council (England and Wales)
  10. mygov.scot — find your council's recycling centre (Scotland)
  11. nidirect — recycling and reusing (Northern Ireland)
  12. B&Q — price check: basin wastes
  13. B&Q — price check: bottle traps
  14. B&Q — price check: sanitary silicone