NHmaster3015
Master Plumber
Sorry, I still say that your As a general rule, all traps need vents.... is a generalization.
No, it's not my rule, every code in this country requires traps to be vented one way or another.
I think you are mistakenly thinking that a DIYer did that plumbing.
We had already established that the only thing the OP did was cut in the san tee and the trap. No clue who did the rest, I only pointed out the code errors there and they are code violations no and's if's or but's about it.
The home owner and the OP of this thread told you he did not do that work and that all he did was add the trap and stand pipe. He also said he bought the house recently and has no problems with the drain system and he had a home inspector inspect it before buying it and none of this was mentioned as not being to code. I can't see any house inspector making that kind of serious error.
Well, apparently the home inspector is not up to speed when it comes to illegal use of fittings and traps. What more can I say here. I can print the code and commentary if you would like.
And now you have told him that he has to redo it all now when he installs his new water filter and softener....
I did not even once tell him that he had to re-do anything. What I said was that had he applied for the proper permit and had he had the installation inspected the code inspector would have made him change those things that do not meet code. What I really don't understand is why you want to make an issue out of what any licensed plumber knows is bad plumbing.