Evening all. We’ve started getting a drain smell in and around our lounge/staircase. For info, house is 15ish years old, 3 floor townhouse with the problem around the middle floor. There is a bathroom and en suite on floor above. I’ve tried an off the shelf drain cleaner for the shower as that is closest to the problem area but it hasn’t helped. Smell does come and go - not sure if I’m going mad but does seem to be worse when it’s windy?! Any usual suspects I can try/look at before calling the pro’s?