mind your p-trap

If you have a shower (or anything that drains to the sewer) that you
don’t use on a regular basis the “P-trap”  will dry up, allowing
fumes that smell like gas to come up through the pipes and potentially
cause one to think that there is some sort of leak and the house is in
imminent danger of exploding.

The good news:
It’s easily and affordably fixed – pour water down the drain.