Is this plumber getting the best of me

[haabbd]

Paid a guy to redo all the drain pipes (not sure what that includes to be honest) under my house (crawl space). Below are pictures where 14 months later sewage is leaking out of what I think is a breather. He came out today and said something is backed up in the drains and this is a water softener overflow and it's doing what it should do.

Can anyone tell me what this is and if it should be there? it is right below the access point (closet floor).
Once pic of the 'vent' where the brown stuff is coming out. The other is the other end of the leaking pipe connecting to other drain pipe.

 

[phishfood]

Is there a vent off of the pipe between the two pictures? If not, that is a violation of most codes.

TBH, that probably isn't what is causing your problem, I think that your plumber is correct in that there is a likely a blockage in the piping somewhere.

The bigger question is what caused there to be a blockage so quickly. Properly designed, installed, and nothing improper sent down,m PVC drainage piping should be trouble free for long periods of time.

 

[haabbd]

No vent. But there is a gap there in the pic where sweage is coming out.
It is at a rental so I cannot confirm anything incorrect hasn't gone down. But the guy who lives there is only there half the month each month.

I just don't trust the plumber. When I hired him to replace the drain pipes I was out of town and in a jam. Charged me $1,400 for what my brother supervised as under 2 hours of work...