Ok, I have read and searched for a while now....I cannot seem to pinpoint the issue I am having so I am throwing it out here. If I missed a "thread" on something like this, sorry, please point me to it.
When I run water in the sinks or tub, I can stick my nose near the vent below in the pic and WHEW! it'll knock your socks off....No idea where the odor is coming from.
I can confirm its NOT coming from the drain. Its coming from that dark hole in the other picture which is the underbelly. Where in the WORLD would that smell be coming from.
I know its not the Air Admittance Valves under the sink since I checked them both with my nose.
This is the picture from the other side of the tub, yes I know the lines are backwards...FR dopes, I am going to fix it later.
This one is looking down into the whole from the picture above.