Slow drain and odd gurgling

The bathroom tub had a slow drain and really odd gurgling. The master bathroom sink draining started fast then really slowed down. Also, a bubble would come back up occasionally. When I got into the crawl space I saw all these connections going in from the side. I know this is wrong because it’s causing the slow draining and gurgling but I couldn’t explain why.
These connections do not look right.

I’m thinking they should coming in from an angle, not at a flat plain.

Is there a NACHI resource, youtube video or resource you recommend to learn how many connections should be connected?

Any thoughts you have are welcome as well.

I referred it to a plumber for further eval and repair/replacement.

Was it vent properly

Agree sounds like a vent problem.

I couldn’t confirm the specific venting for the connections. I suspected that venting is an issue because of the slow draining/gurgling.

Was it just in the bath tub and bath sink. I have a drain in the bath tub that starts to gurgle and slow down just before the drain stops completely and then I have to snake it.(hair) After I snake it ,it runs great until it happens again. My venting is OK

Mine to. :mrgreen::mrgreen:

Sounds like a partial obstruction.

ALL plumbing runs need to have between a 1/4" (min.) and 1/2" (max.) slope to drain properly. You ain’t got that.

Also try flushing the vent ,

Quite the notch cut out of that floor joist, too…

I cannot tell from the pic but sounds like a lack of plumbing traps.