I am replacing a tub and have opened a can of worms in the process. This is all pre-existing work, so I am not looking to redo it at this point, however I'd to keep water out of that vent line. When I cut it open, it had water inside, and it has no place to go, since the vent line simply goes up and through the roof about 10 feet downstream. Before I touched this, it was simply connected together with a very small bend, not enough to stop much flow.



Edited 1 times.

Put the link to the image on here, you can't upload the picture directly

Thanks, I've linked the image now.

The vent should be sloped downward toward the drain, and up as it moves away. Your diagram isn't very helpful unfortunately. Something really can't be both 'up through the roof" and downstream at the same time. I would define downstream as away from the point of origin in a gravity flow system, and up as the opposite direction to the earth's gravity (because some people here like to nitpick about the definitions of terms used here).

by your drawing, the vent is a couple of inches below the drain.
if that is the case, it is totally non-functional and might as well not be there.

The drawing is a cross section. The vent is not connected to anything, it simply runs 10 feet out and then goes out the roof. From the cross section, you can see it is lower than the drain it was connected to.

Would a loop vent be a possible solution?

no

a loop vent is an EXCEPTION specifically for an 'island sink'

==============================================

"Measure Twice & Cut Once" - Retired U.A. Local 1 & 638

a loop vent must have its lowest point drain back into another drain. it can't work if it is full of water..

But if the loop is high enough, I'm thinking water could never rise over the crest to flood the line that ultimately leads up to the roof? Even so, I don't think I can make the loop very high in this application. I am thinking about putting this back how it was, as I can't afford to redo all of this back to the stack. This tub gets extremely little use for me to start ripping apart floor and wall to do this the right. I am thinking either studor valve or tie these two lines back together with a loop a little higher than what I found. I should have never looked at what was going on under the floor since it was technically fully functional.

If your drawing is accurate, you might as well NOT connect it back together because it will be completely useless, so save your effort. IF we were there, we might be able to do it correctly.

I hear you. If we could tear up the floor and wall, this would be much easier. Alone, the drain line is perfectly fine, and the vent nicely runs up and out the roof, it's just these horizontal runs in the joist (8 feet from the wall) are poorly positioned -- with the vent running 4-5 inches lower than the drain run. Wish I knew what the original person who did this was thinking. I can't afford to turn a tub project (which was working perfectly fine in the few times it is used) into something bigger. Trying to take this from "really poorly done" to "sort of ok" while I have it open, but seems no quick solution to this.

Here is a photo of what was previously connecting these two lines together:

And a photo of the lines inside the joist:

Whoever installed that was completely incompetent and makes you wonder what else he did not know how to do corrrectly.