Why does a bad sewage smell come from a bathroom sink in the house after we run the water in the kitchen sink to do dishes And it doesn't always happen..but does when the water runs awhile?

Answer 1

There are two possible causes here. Either your sewerline has a slight blockage causing the smell. Otherwise your sewerline is not venting properly, however this would only happen unless a new installation has been done, because you would have noticed it before. My recommendation would be to get the sewerline checked and it may need to be rodded or flushed out with a high pressure hose to clean it properly. There is a possible third answer. If there aren't many occupants in the house or, the house is quite large for the number of people actually living there, or possibly the occupants travel often then the "p" traps(curvy pipe under the sinks below the drains) could be drying up allowing sewer gasses to vent from the drains. If you haven't spent the money on a plumber yet, then try pouring a quart of water down the offending drain first, if that solves the issue then you have saved the cost of a plumber, No offense to plumbers.