Sewer Smell from Bathtub drain
This has been an ongoing problem since I bought my house 9 years ago. I've had 2 plumbers look at the problem and didn't really have any ideas.
The smell comes from the shower drain, main floor, basement underneath. I do hear some gurgling in the drain if I flush a nearby toilet, which leads me to believe that the trap is being siphoned out.
I have checked the vent on the roof and it seems to be clear.
I'm wondering if there is something incorrect with the way the plumbing was done when the house was built?
Any ideas would be greatly appreciated!