vent and whole house trap

Assuming all fixtures are properly vented, is there any need for a vent just before a whole house trap? I am not thrilled about having a whole house trap and may remove in the future, but current there is a open piece of pipe (pointing up) in the basement just before the whole house trap. I am not sure if it should be capped or a pop up vent or vented to the outside. Is this vent letting air in or out? (Guess I can check that with some saran wrap over if).

You shouldn't have any open pipes in the house.
I would assume it is a drain pipe for a future bathroom if needed.
You can cap it of with a test or permanet cap.
It would let air in and out and the in air you don't want.

We remove house traps every chance we get. We usually find out when trying to clear the drain and the cable tries to punch through the second cleanout cap.....leaving the obstruction beyond that remaining.

If you are required to have a whole house trap, then yes, it does require venting on it's downstream side. Such a vent serves to ventilate the city's sanitary sewer system, and to equalize pressures between it and your "hopefully" properly vented plumbing system.

And yes, it should vent to the outside.

vent

OK, when you say downside I assume you mean between the whole house trap and the septic. But no need for one between the fixtures and the whole house trap. (The fixtures are properly vented, this would be an additional vent just before the whole house trap).

Correct.