We live in an high rise apartment building and every now and then we can smell mold from our bathtub drain for about 3 to 4 days then it goes away for a few weeks. We are also getting a nasty rotten egg sewage type smell from the bathroom sink. No one in the building is supposed to have a washer in their apt but our upstairs neighbors do and when they wash their clothes it bubbles up through our drains. Could that be where the smell is coming from?
We have checked the drains for hair but do not see any, I have poured bleach and hot water down the drains several times.
What do we need to do to get rid of this nasty smell?

CNL