would it be a problem if I covered/seal off the bathtub overflow? We’ve been here 30 years and have never needed the overflow for the bath tub.

I know that some bathroom sink designs have a history of smelly overflows, with material getting caught up in the overflow tube. I guess it is possible. With a tub overflow, it is not like you can use a turkey baster and put something down the overflow to attempt to clean it out, right?

I would contact the tub liner people and ask them what is possible. Maybe there is something that came disconnected and did let some water in. I would start there, especially if there is a chance that the tub liner is still under warranty. You don't want to risk having them say that something you did to try to fix this is voiding your warranty, so call them, first.

@Nancy We had the liner put in 16 years ago, the company is now out of business. I’ve used several tools to get anything in the over flow out. I’m 99 percent sure the smell is coming from the area where the new liner and old tub meet at the overflow. About 6 months ago I pulled all the caulk that was put between the old tub and liner out And placed it with new caulk. That kept the smell away for awhile....but it’s back now. We bought it from Bath Liners Direct. In my research I found out that they are still in business but under another name, that way they don’t have to honor their lifetime guaranteE. I’m not sure how true that is, but it does make me wonder

Yes, warranties are useless when the business goes under. I learned that the hard way with a landscaper. I hope others pop in with more ideas for you.

"We had the liner put in 16 years ago"

Maybe time to think about a new tub. Those liners definitely have a limited life span.

I would fill the tub, put in some bleach and let the water run so it flushes out the overflow. The overflow should connect to the drain. Maybe it is the drain and the smell is stronger in the overflow. Other options........baking soda and vinegar instead of bleach so it gets a bit scrubbed in their. I have tried that with a stinky drain. You can put baking soda into the over flow hole and pour vinegar in.