Quite probably the first thing you’ll know about a leak is seeing a damp patch on the ceiling below the bathtub; or a complaint from someone in the apartment below yours, about damp patches or even worse water dripping into their apartment.

If you suspect you’ve got a leaking bathtub drain then it needs investigating and dealing with immediately. If not, it will only get worse and could result in a lot more damage to the ceiling or floor that the bathtub is above; which in the long run will cost even more to put right.

Finding the Problem

The first thing to do is to remove the side panel of the bath tub and immediately mop up any moisture, then with some cloths dry the underside of the bath and any pipe-work/fittings that you can see are damp. Next, make sure you’ve got a flashlight ready, put the plug in the bathtub and allow a small amount of water collect in the bath - a really small amount of water.

Release the plug and look to see where the leak is occurring. If you can’t see a leak occurring, repeat the process but this time put some sheets of absorbent paper under where you suspect a leak might come from.

Sometimes you can’t ‘see’ a leak - but can at least identify where it’s likely to be. You could also try increasing the volume of water with which you’re testing for the leak. The leak might be occurring at a point in the pipe-work that a small volume of water can’t reach.

Fixing the Leak

There are several points at which a leak could occur in a bathtub drain system. Some can be repaired but others may require purchasing a replacement part. The following are some of the most likely causes of a leak in a bathtub drain and presume that you’ve got plastic drainage pipes to work on.

It is very rare for plastic pipe to just crack. However, should this be the cause of the leak simply cut off the cracked and leaking section and replace with it with a new one. To install a replacement plastic section you’ll need to add compression joints to both ends.

A more likely cause is a leaking joint. First you should check that it’s not just a question of tightening the joint to solve the leak. Check the washers on the inside of the joint, if they’ve perished it might be possible to just buy a replacement one to solve the leak?

If that doesn’t work you’ll need to replace the joint. Again this is most likely a compression joint which should twist and pull off quite easily. If it doesn’t it could also have a plastic solvent weld. If you can’t disconnect the joint you’ll have to cut off a short section of pipe either side of the joint, then continue with the repair as if it were a cracked pipe.

If the problem is in the waste trap, or sump, of the drainage system it’s probably best just to buy a new one and replace the old unit. Before doing that you can again check the unit for tightness and that it’s not just a washer that has perished.

If the problem is with the waste fitting in the bathtub itself, you’ll first need to disconnect the pipe-work underneath the bathtub. Then having extracted the fitting clean it thoroughly and inspect it for any cracks.

You might be best off just replacing it with a new one whether you find a crack or not. However, the leak could be due to the sealant that is used when seating the fitting, deteriorating over time. If that is the case then all you need to do is to apply some new sealant, like mastic putty, and replace the fitting in the base of the bathtub.