There could be a couple of reasons, but the most likely is that the water traps in your tub/shower, sink or toilet are not working properly. A water trap (pipe looks like the letter "J") blocks the sewer smell from coming up... Maybe there is a leak in one of your J-traps?
I recently stayed at a hotel that had exactly this problem, except it wasnt a leak... When a neighboring room would flush the toilet, it would create a vacuum and suck the water out of our trap... we just had to run the water a little to refill the trap. posted by
DulceDeLeche (205)
You have a sealed waste trap under your bath, sink and toilet.The sewer smell is sealed from the room by a water seal inside when this drys up it allows the pipes to be open for the smell to waft in.
Many times the pipes in the sink or bath can get plugged or backed up which will cause the smell to come back into the house. Try using a snake or some drain-o and evaluate if the smell still exists.
Your bathroom is probably smelling like a sewer because the toilet hasn't been cleaned properly or hasn't been cleaned in awhile. Another solution might be to flush the toilet paper, sometimes when you leave it in the trash can it also causes a fowl Oder.
Clean the drainage pipeline regularly.If your house is an old one it may cause some troubles like this.As for as possible keep the bathroom airy by keeping the doors and wondows or ventilator open.
This smell comes when there is no air circulation,so fix an exhaust fan.