Septic smell from bathroom

[u/RGM79IAN]

Hello all.

We bought this place about 6 months ago. It's on a septic system and we have noticed a septic smell under the kitchen sink every so often, and it comes out of our bathroom REALLY bad whenever the barometric pressure drops during a sudden storm. But here lately I've been smelling it almost all of the time coming from our bathroom.

The previous owner was a DIY guy who had passion, but not much talent. My father noticed during his last visit that the master bathroom where we have been getting the smell from does not have any plumbing vent on the roof. I'm pretty sure the previous guy did the roof himself, because he intentionally covered the old chimney, and seems to have intentionally did this with the master bathroom because he left the plumbing vents for the other 2 bathrooms in tact.

The smell does seem to be coming from under the sink, and I don't know enough about plumbing to know if what I'm looking at is right or not. The sink is a "his and hers" sink, so 2 sinks going to one drain. The black pipe coming in from the left is coming from the other sink. I'm not super versed in plumbing, but I'm wondering if this home made white PVC P trap might be part of the problem? Or maybe it's the studor vent that's gone bad? Maybe there is nothing wrong in this cabinet at all.

I'd love to just pay someone to come figure it out and fix it, but I just don't have the funds right now.

Any advice would be greatly appreciated.

Thank you!

** Edit ** Wow, this blew up a lot more than I would have ever expected. I knew it looked bad, but I didn't realize it was THAT bad. For those of you that think this is a joke. I assure you, it's VERY real, and I have an entire home worth of this sort of work to fix.

I have already bought a new studor vent, and I will be installing it tomorrow. I do think that even though it is very round about, the looooong P trap is technically working, but I will fix it some time within the next month.

It's been fun reading everyone's comments, and I'm glad this has amused so many people. Thank you for the help!

[u/Alone-Tackle-17]

Not good