How do I replace a bath waste and overflow?

A bath waste kit is one component that seals in three separate places: the flange to the bath, the banjo to the waste body, and the overflow hose to the banjo. A leak from any of them arrives at the same place on the floor, which is why replacing the whole kit is often quicker and cheaper than chasing which part of a twenty-year-old one has gone. The drawing shows the full stack exploded, in order.

Safety

What you'll need

• A complete bath waste and overflow kit to suit your bath
• Sanitary silicone
• Water pump pliers or a waste key
• A shallow bath trap if you are replacing that too (optional)
• A torch and something to lie on
• Silicone remover and a plastic scraper

Step by step

1. Get proper access first.Take the bath panel off. If the bath is boxed in and tiled, this job is the reason to cut a proper access hatch rather than working through a gap — you cannot tighten what you cannot reach squarely.
2. Check what you are buying before you take anything apart.Look at whether the existing overflow is a flexible hose to a banjo or a rigid pipe, and whether the plug is a chain plug, a lift-and-turn, a click-clack or a cable-operated pop-up. Take a photograph. A universal kit fits most baths but the plug type has to match how you want to use it.
3. Turn the water off and clear the trap.You are not disturbing supply pipework, but do turn off the bath taps' isolating valves if they exist, so nothing is dripping into your working space. Put a shallow tray under the trap.
4. Disconnect the trap and the overflow hose.The trap unscrews by hand from the waste tail. The overflow hose comes off the banjo spigot — sometimes a push-fit collar, sometimes a jubilee clip. Expect stale water in the hose.
5. Free the backnut.Hold the flange from above with a waste key, a pair of crossed screwdrivers in the grating slots, or long-nose pliers, and turn the backnut underneath. If the whole assembly spins, put more downward pressure on the flange. If it will not move at all, warm it or cut the tail off with a junior hacksaw and lift the flange out from above.
6. Clean both seats back to bare surface.Scrape and dissolve every trace of old silicone and putty from the bath around the waste hole and from around the overflow hole. New sealant does not bond to old, and this is the single commonest reason a new waste kit still weeps.
7. Bed the new flange.Either a bead of sanitary silicone under the flange or the flat washer supplied with the kit — one or the other, not both. Never plumber's putty on acrylic; the oils in it attack the plastic over time.
8. Build the underside stack in the right order.Large rubber washer with its flat face up against the underside of the bath and its tapered face down; the banjo, rotated so its spigot points towards the overflow hole with no strain in the hose; the second washer; then the backnut. Getting the washer the wrong way up gives a joint that seals on a narrow ring and drips.
9. Tighten by hand tools only, and evenly.Hold the flange still from above and bring the backnut up until the washers are visibly compressed and the flange will not turn. That is far less force than most people apply. Wipe the silicone squeeze-out from inside the bath while it is still wet.
10. Fit the overflow plate and hose.Gasket behind the plate, plate screwed through into the overflow body, and the hose run in a gentle curve with no kinks and no tension onto the banjo spigot. A hose stretched taut pulls the banjo out of alignment and starts the next leak.
11. Fit the trap and test properly.Hand-tighten the trap. Then fill the bath right up until water is running steadily out of the overflow, and leave it. Watch the whole assembly with a torch. A jug of water tests the waste and tells you nothing at all about the overflow, which is where these kits actually leak.
12. Leave the silicone to cure before the bath is used.Give it the full time on the tube — usually 24 hours — before anyone bathes in it, and check again with a torch after the first real bath.

Common mistakes

• Using plumber's putty on an acrylic bath — The oil content attacks acrylic and it eventually crazes or discolours the shell around the waste.
• Tightening the backnut with grips as hard as it will go — It crushes the washers out of shape, distorts a thin acrylic shell around the hole, and can crack a steel bath's enamel from behind. The washer seals by contact, not by force.
• Testing with a jug and putting the panel back — It only ever tests the waste. Overflow leaks appear the first time somebody has a deep bath, by which time the panel is sealed back on.
• Fitting a standard-depth trap under a bath — There is rarely the height for it, and forcing it means the trap ends up strained or the bath ends up lifted. A shallow bath trap is the correct part.

Questions people ask