This could be the ceiling vent to outside having a kink in it, water/moisture gets trapped and goes stagnant and smells after a while.
Thanks dubgem, it's worth checking out. I'll make a list of all the possible causes from this thread, give it to the plumber and ask him to check them all.
We use cookies and similar technologies for the following purposes:
Do you accept cookies and these technologies?
We use cookies and similar technologies for the following purposes:
Do you accept cookies and these technologies?