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Hello, any ideas on how to solve this?
After using the sink in the ensuite, the room fills with a pungent drain smell.

So far I’ve done the following:
1. Used a bottle of drain unblocker.
2. Used baking soda / vinegar
3. Removed U bend and cleaned it.

Neither of these have resolved the issue. When cleaning the U bend, the pipe was lined with a horrible black slime which I’ve removed, it may be covering the pipes I couldn’t reach.

Any ideas or experience of how I could fault find / resolve?

Thanks,
Ewan

hi, yes!

i presume you live in a new build and the plumbings done by unqualified builders and dumb architects!

you will have a Durgo valve behind boxing or posib;y exiting the loft space. this you will find is probably stuck as it is supposed to pop up breifly to release vacuum then quickly shut preventing rising sewer smell. if this does not happen, then it sucks the water out of the trap (usually in the shower). you cn proove this by sealing the shower trap temporarily with say a plunger over the top of the shower drain, you will find it no longer smells. its possible but less likely it is the basin trp doing the same.
other than this, the durgo valve is behind boxing in the same room.
or:
you have one of these under your basin, the gland jams open with debris or age.....
https://www.toolstation.com/viva-magna- ... lve/p82878

hope that helps?