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?