DIY Doctor

Slow draining bath after sink fitted

Postby sipickles » Wed Jan 21, 2009 1:09 pm


I have just done a complete bathroom refit and it has generally been a success.

I do have one small issue though, and hoped someone might have a suggestion.

When I fitted the new bath, I had to change the plumbing to get it to fit the old waste outlet (due to the new position of the bath plughole).

The bath drained fine.

When I connected the sink waste, which shares the same waste outlet pipe, the bath started to drain slowly. Disconnect the sink bottle trap and the bath drains quickly again.

Since it seems to be something to do with the air flow into the sink waste pipe, I replaced the sink bottle trap with an 'anti-syphon' one.

This doesn't seem to have had much effect tho.

Can anyone suggest any solution?

Many thanks

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Postby TheDoctor4 » Wed Jan 21, 2009 4:42 pm

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Postby Stelf » Wed Jan 21, 2009 7:37 pm

Hi Simon,
First of all you should, if possible, run separate waste pipes from the bath and basin. They do work much better and will solve your problem at a stroke. As the waste water from the bath runs past the basin connection it is sucking in water, and eventually air from the basin which will slow down the rate of flow. Connecting the basin waste pipe may also be introducing a backfall in the waste pipe from the bath, if not done correctly, which could also be part of the problem. Run them separately and all your worries will be over.
Best wishes
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