I just wanted to know if plumbing pipes that are just for air.. they need a slope?

Hi,

Although horizontal level vent pipes are permitted as minimum code, sloped vent pipes @ 1/4" per foot of fall towards the fixtures is best. So absolutely a YES.

So we don't slope the hole line just the part that near the fixture?

Hi,

You must slope from where it is tied into to either a branch vent or through the roof. Basically if there is some liquid in it, it will drain off.

OK so the hole line must be sloped in case there is water that will fall in to the pipes

Yes, so it won't reduce the capacity of it. You want the full capacity of the vent to fuction.

Thanks u so muchh!