Mobile and manufactured are under hud rules first so…
Is it original?
What are local rules?
BTW I didn’t look at picture or read your post.
Now onto the question asked…
Use common sense.
The standpipe should have a trap and venting in the plumbing world.
This trap isn’t doing anything beneficial. This was probably for something that was never finished or the installer had to be a “moron”. Pardon my French.
Manufactured and Mobile can get complicated. Understand the rules first in the U.S. because tradesmen don’t like working on them because of the rules. You may want to consider not inspecting them “in my opinion”
My comment is getting winded and open to opposition.
HUD rules, local rules, even “park” rules etc. Play a part in how things “should” be.
This “should be” done over