T.F.
Do you have a snake? It is a long wirey things that winds down into the drain and can push out the clog or whatever is smelly.
We actually rent a big electric one from the rental place about once a year and hubby does this theough the outside drain to keep things clear.
Another option if your hubby is handy is to turn the water off, take the pipes apart and clean them then re-install.
Is it the garbage disposal? I will sometimes put a dishwasher tablet in there with hot water and run the disposer.
Hope you get it worked out!