Venting, and pipe direction?

Hi folks!
I'm working on replacing my unvented/untrapped(!) 90 year old laundry tub and plumbing in the basement.

I'm able to tap into an existing vent which I brought down through a wall from the kitchen on the main floor during kitchen renovation a few years ago, in anticipation of reworking the plumbing in the basement laundry.

So here's my predicament.
I've got a few obstacles in the way of beams to work around, and the only real way I can run this vent is by elbowing it down, and later to go back upwards vertically before dropping it back down towards the fixture further downstream.

In essence, if it were carrying drain water, it would be a massive trap, with six inches of height and 8 feet wide. But - its a vent - its not carrying _waste water_, its only carrying _air_!


So i'm wondering - are we allowed to to have a vent pipe drop 'down', only to come back 'up' ?

Hypothetically, the only risk I see is condensation forming in the pipe, and over years sooo much condensation that it would fill up a few gallons of water to fill an 8' stretch of 1.5" pipe.

Other stretches of the vent line would all have proper drainage points for such condensation including the long vertical line which goes from second story through kitchen into basement. Its really just a mid-portion of the vent line which I have to run about 20 feet across the basement.


Any advice for this handyman is appreciated !
Thanks.

The ONLY answer to your question is NO! If you create a trap, it WILL fill with water, and once that happens you no longer have a vent, you have a blocked vent with no way to unblock it.