Smoke Test?

We have a new addition of two years. For the past three years, one of the two sink areas have a bad smell like wet gym clothes. The toilet has a strange fishy smell. We have flushed it with chlorine bleach, baking soda and vinegar, toilet bowl cleaners, and bio clean.

I've tested the plumbing vents by pouring down lavender oil for leaks. If there were any leaks, we should've smelled the lavender. I've checked in the crawlspace for leaks and odors there, and in the attic, but found nothing unusual. The smell gets worse when it's cold out.

Has anyone had anything similar? Or any suggestions?

After reading this thread, we checked all the electrical outlets, but they appear to be fine. Was the lavender oil not enough? We are considering doing a smoke test. Could anyone share with me their experience?

Thanks!

Lavender oil? I know peppermint extract or smoke test. It can be many reasons for bad smell (wax ring, AAV, vents....and the list go on). Do yourself a favor, get a professional plumber to test your sanitary lines and vents and be done with it.

Lavender is not strong enough. You need a professional for this problem.

Thanks for the replies. Would you say the smoke test is worth it?