Bath Waste Leaking

The parts of a bath waste, and what fails

Knowing the names helps when you buy parts or describe the fault. A standard bath waste has a plughole fitting with a chrome flange on top, a rubber or fibre washer under the flange, a second washer under the bath, and a large backnut that clamps the two together through the bath. Below it sits the trap, 40mm, usually a shallow-seal type because there is little room under a bath; Approved Document H allows a 50mm water seal on a bath trap rather than the 75mm needed on a basin. The overflow is a separate plate at the head end with its own gasket behind it, joined to the waste by a flexible corrugated hose, often called the overflow banjo where it connects.

Pop-up and click-clack wastes work the same way underneath, but add moving parts. On a pop-up, turning the overflow knob lifts the plug through a cable or rod running down the overflow hose. On a click-clack, pressing the plug locks it up or down with a spring in the plug itself.

The washers are what wear out. Hot water and time harden them, and baths flex as they fill, so the clamp slowly loses its grip. Overflow gaskets fail quietly because the overflow is only tested when someone fills the bath to the brim.

Which part is leaking?

With the bath panel off, dry everything and lay kitchen roll under the plughole, along the overflow hose and under the trap. Then run these tests in order and watch for the first wet patch. If you have not got the panel off before, or you are not yet sure the water is from the waste at all, start with finding a leak under the bath.

• Put the plug in and fill to about 10cm. Leave it 20 minutes. A drip from under the plughole flange means the washers or backnut.
• Keep filling until water runs into the overflow. Water appearing behind the overflow plate, or along the hose, means the overflow gasket or the hose joints.
• Pull the plug. A drip that starts only while the bath drains is a trap joint, the waste’s threaded tail into the trap, or the pipe beyond it.
• On a pop-up waste, check the knob lifts and drops the plug cleanly with the bath empty. If water then appears around the knob body once the bath is filled to the overflow, its internal seal has failed.

If the floor under the bath is soft, or a ceiling below is stained, do not keep using the bath while you wait for a fix. Every drain empties a full bath past the leak.

Fixes you can try, and where they go wrong

Trap joints are hand-tight plastic compression nuts with a cone or flat washer inside. Undo the nut, check the washer is seated straight and not split, refit and tighten by hand plus a quarter turn. Overtightening cracks plastic nuts. A new bath trap typically costs £4 to £15.

A plughole seal leak needs the waste taken out. Hold the flange still from above with a waste key, or the handles of a pair of pliers pushed through the grid, and undo the backnut from below. Clean off every trace of old washer and sealant from the bath, fit new washers the way round the kit shows, and tighten the backnut firmly without twisting the flange. Some baths need a thin bead of sanitary silicone under the flange as well; follow the bath or waste maker’s instructions rather than guessing, and let it cure before filling.

Overflow leaks are usually the gasket behind the plate or a split in the corrugated hose where it bends. You cannot patch that hose reliably. Buy a complete waste and overflow kit, which typically costs £15 to £60 depending on the finish and whether it is a pop-up, and replace the lot so the plug, overflow and hose all match.

The real obstacle is access. Many baths are boxed in so that the waste end is hard to reach, and some are tiled in with no panel at all. If you cannot get both hands on the backnut, you will not get a good seal, and forcing it risks cracking an acrylic bath around the plughole.

When the leak is more than a washer

Some waste leaks are a sign of something else. A crack in an acrylic bath around the plughole, often from a backnut overtightened in the past or a bath not properly supported on its feet, lets water past no matter what washers you fit. Look closely at the plughole with a torch; hairline cracks radiate outwards. That needs a bath repair or a new bath, not a waste.

A bath that sags because its feet or cradle were never adjusted will keep tearing the seal and the waste joints. If the bath moves when you step in, the feet need adjusting so each one bears firmly on the floor before anything else. A waste that drains slowly and then leaks at the trap may have a blockage further down that is backing water up past the joints, which is covered in a leaking waste pipe.

What a plumber does

On a visit, a plumber confirms the leak point with the same fill and drain tests, checks the ceiling or floor below for how long it has been going on, and replaces the waste and overflow as a set rather than chasing one washer. On a tiled-in bath they may need to cut an access panel into the side, which they should agree with you first. If the bath needs lifting, the taps and waste are disconnected and the seal to the wall has to be redone afterwards.

For a waste you cannot reach or a leak already coming through the ceiling, book our leak repairs service. The £60 call-out covers the visit at any hour and the repair price is agreed with you on site before any work starts. If a ceiling below is already wet, read a ceiling leak below the bathroom while you wait.