sewer odor in bathroom sinks

[cornfed]

We have double bathroom sinks. Occassionally but, not constantly there is a sewer like swell coming from them. Help please on how to resolve.

[kok328]

While I would fully expect the two sink drains to be tied together, it may be that they have separate drains. The P-trap under the sink is designed to keep sewer gas from backing up into living space.

I suspect that the sink less used has a dry P-trap.
Simply run the faucet to refill the P-trap.
Also make sure that the toilet and tub/shower have water ran in them regularly to keep the P-trap full.
The other possible cause is that you have well water which can sometimes emit a sulfur (rotten egg) smell. There really is no cure for this but, sometimes a water softener can eliminate some but, not all odor.