Is this branch drain correct and what is this cap on my vent?

[Rocknroj]

The pictures show a drain line from a lav.. pitch is perfect on the horizontal for just under 5 '. then it makes a downward bend to the horizontal drain. It uses a short elbow, a few inches of pipe and a sideways sanitary 'T'. From what I read a sanitary 't' is not the correct fitting on the horizontal. The drain serves 2 lavs from 2 separate 1/4 baths. I am not sure how/if they are vented .

Would the sharp change in pitch cause siphoning? Is the San 'T' legal?, what about the sharp turn 90.

 

[FullySprinklered]

Looks like two octopusses had a wrestling match and the plumber lost.

 

[Sponsor]

 

[Cacher_Chick]

You are going to have to tear all of the walls down so we can get a better look.

 

[FullySprinklered]

Excuse me. Octopi, but the jury's still out, they say.

 

[Kreemoweet]

Doesn't look like a Sanitary Tee to me, more like a Combo (Wye+ 45* bend). Long-turn 90 is
technically required, but I doubt it will cause any problem with just lav drainage. There's
nothing wrong with that change of pitch. None of
that stuff will cause/promote trap siphonage, but lack of venting surely would.