I have just purchased a brand new home. It has sat empty for 2 years and is a builder's foreclosure. I am having a problem with a sewer smell. I have made sure there is water in all of the drains, and once I noticed when I have the hot water running in the bathroom sink, the toilet bubbles up. The smell is not constant. I have only one pipe running out of the roof (I have 4 bathrooms) and it seems most of the baths are vented out of the sides of the house. Is this correct? How do I find out where the smell is coming from and what can I do to get rid of it?