In the 1st floor slab bathroom, hissing air comes out of the sink drain whenever the central heat comes on. In addition, the air that comes out, of course smelly like sewage.

Now, I know I can do the bleach procedure, but what I don't get is why the air is flowing. There is a p trap in place, and the sink is used regularly, so it is not dry.

How do I stop this?

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Originally Posted by tulane87

In the 1st floor slab bathroom, hissing air comes out of the sink drain whenever the central heat comes on. In addition, the air that comes out, of course smelly like sewage.

Now, I know I can do the bleach procedure, but what I don't get is why the air is flowing. There is a p trap in place, and the sink is used regularly, so it is not dry.

How do I stop this?

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Something's terribly wrong here. The air handler or furnace fan appears to be pumping air into your drainage system. Shut the stopper on the lavatory and seal off the overflow with duct tape and get someone in to check it. Sewer gas is entering your home and that's a health hazard to you and your family. Block off those outlets and get help.
I would call in a heating man first as it seems to be more of a heating problem then a plumbing one. In all of my, over 50, years of a plumber this is the first complaint that I've ever had of this nature. Please keep me in the loop on this. I want to know what's going on with the repair and what you find out. Good luck, Tom