Basement Smell in Utility or Bathroom?
It sounds like a P-trap to me, one thing I learned years ago, water evaporates, thus the reason you have to re fill the P-traps.
Try pouring some vegetable oil in the P-trap at least enough to fully coat the surface this keeps the dry air in the house from pulling the moisture out of the traps, the plumbing side is very humid so it is not taking water out of the traps. I have had the same smells but after adding the vegetable oil to the floor drain, Sink and shower I did not have this problem in that house.
Since then if we have a mud room I put oil in those floor drains , in my last home we had a bathroom that wasn't used except when the family was home that sink and shower got a good shot after the first time we thought something died in the house , opened the bathroom door there was the smell. It never happened again with liquid vegetable oil, never had a bad smell from the oil.
One person, a snow bird I told about that, even used it on her toilets. I have not had an issue with toilets but if I was going to not be there for an extended time I would probably add to the toilet also.