Sink sealing washers.

The latter.

Sometimes there's a compressible foam washer for inside the basin, more often nothing is provided. A leak here just means the basin will slowly drain when the plug is in -- it doesn't leak though. If this is an issue, you can put a line of silicone inside the basin around the basin drain under the waste flange.

Below. However, use silicone sealant both under the plug hole and between the washer and the bottom if you want any chance of a good seal.

Christian.

I could be wrong, but I suspect that the OP is talking about a single skin kitchen sink (stainless steel or plastic) rather than about a bathroom washbasin with built-in overflow.

If he *is*, I would put the rubber washer *inside* the sink, under the flange of the waste fitting.

The problem there is that the washer pushes the waste up so that you sometimes, depending on the pressing and the thicknesses of the components, get a sharp lip from the edge of the waste. This collects solid waste and prevents all the water draining away.

Christian.

All of my SS sinks are a bit dished where the waste attaches so that, even with a thin rubber gasket under the waste flange, the top of the flange is still lower than the surrounding sink area.

Yes, it depends on the depth of the dish and the thickness of the washer. When favourable, I doubt there is a real problem.

However, even at best, I prefer metal to metal contact, to reduce the amount of filth that can hide invisibly between them.

Christian.

But doesn't the filth then hide under the flange?

Ok, fitted a kitchen sink an hour ago... Instructions went... Drain-hole, sink, rubber washer, back nut. With silicon between Drain-hole and sink.

Found the method on uk.d-i-y too! Regrettably cannot find the original posting on Google, but whoever's suggestion it was is a genius!

Plumbers used to use lashings and lashings of Boss-White before this new fangled silicone stuff.

DG

Doesn't the silicon cause problems if you ever have need to remove the waste?

Silicone's pretty weak in tension.

Christian.

But if it's adhering well to both surfaces, it's an *absolute abstrad* to break the joint. It's used to glue glass fish tanks together, for example.

On Mon, 12 Sep 2005 10:55:50 +0100, Chris Bacon scrawled:

Different type of silicone. If you used normal 'silicone in a tube from Wickes' to assemble a fish tank you'd have a wet floor.