Cimorene

Gas build up is sometimes a problem in a guest bath in this house,because it doesn't get used enough. As you say, it happens because the u-bend dries out and won't keep the gas out any longer. Will letting the water run for a while or flushing the toilet help out the problem?

That will fix it here, but of course, this is a single family house. i can't imagine how awful it would be to live with that all winter. Blech!