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I've just fitted a new basin waste with a plug in a chain. I've tried with the supplied washers etc, and with plumber mait, and have the same results each time. The seal holds whilst the plug is in, however if I run water without the plug in or when I release a basin full of water, I get a significant leak coming out directly under the sink.

The waste has a hole either side for the overflow (seems fairly standard?) and I have lined this up with the overflow at the back of the sink, but it seems that when I release water down the plughole, it is coming out of these overflow holes and then travelling down the outside of the waste.

Despite watching many YouTube tutorials, I can't figure out what I'm doing wrong!

  • Could you edit and add a picture of the underside of the lavatory. – Jim Stewart Oct 12 '18 at 14:54
  • What country are you in? Plumbing fittings and techniques are country specific. – Jim Stewart Oct 12 '18 at 15:02
  • I'm sorry, I'm trying to add a photo but it's not working. I've added plumbers mait to the underside as well as the top, and that seems to have stopped the leak. I'm just slightly concerned that the water is still leaking internally, but now I've blocked it's way out if that makes sense. I'm in the UK. The sink does have two layers, and the holes in the waste are sitting between the two layers as you said they should be. – Claire Oct 12 '18 at 15:46
  • The waste is this one: screwfix.com/p/basin-waste-with-chrome-plug-chain-10-/… – Claire Oct 12 '18 at 15:47
  • Oh, and it's a sink basin, rather that a lavatory – Claire Oct 12 '18 at 15:47
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The holes in the drain are supposed to be "inside" the sink. Most china bathroom sinks have a double bottom in the region of the drain. The holes in the drain for the overflow must be inside the cavity between the two bottoms. The holes in the drain cannot be outside this cavity or water will pour out when the sink is draining.

Some bathroom lavatory sinks are single bottom and have an exposed overflow tube conducting overflow to the drain. These may require a different kind of drain. You may have a mismatch between the sink and the drain.

EDIT

You cannot (permanently) stop a drain leak from the outside using plumbers' mait (putty) . There is something mismatched and the leak can be expected to reappear. Consult someone in the UK. They will quickly recognize the problem.

Perhaps the seal you are using on the bottom (outside) is not the proper one for this application. I think this seal is supposed to be conical on the end to protrude into the cavity. This causes it to tighten around the drain when it is compressed. Or the holes in the drain are too far down to be fully enclosed by the cavity around the drain. Perhaps there is more than one type of drain and you are fitting the wrong one.

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