Vent Stack Leak Question

I can't figure this one out...

I have two vent stacks that run up through the roof. There is no sign of a problem with the flashing. Just above the attic floor (about 2 feet below the roof) there is a fitting that looks like a coupling on both stacks. Both fittings have a slow leak. Are these fittings some type of "check valve"? Otherwise, I would think any snow or rain water that entered the stack would simple drain through the waste line.

And, ultimately, how do I stop the leaks?

thanks!
Stratham

What do they look like?
A black neoprene rubber sleeve with two stainless steel hose clamps (aka Fernco coupling)?
A stainless steel sleeve with rubber sleeve inside with torque screws (aka ho-bub or Mission coupling)?
If either, they're just couplings (not a check valve...wouldn't have anything like that in a vent).
Just tighten the screws. Should stop them from leaking.
Good luck!
Mike

As previously noted, just tighten the clamps on the couplings. Rain and snow will get into you vent and will drain out. This is normal and doesn't hurt anything. Are you sure it is the leaks are from the couplers and not getting past the roof jack?

They're white PVC that look like a standard straight coupling sealed with PVC primer/cement. The strange part is on one stack it is about 2 inches directly above a T joint so it didn't facilitate the installation of the final length of the stack that extends up thru the roof.

I'm certain the leak isn't coming from the roof. I can see the water slowly bead up on the joint of the coupling rather than running down from the roof jack.

thanks-
stratham

Make certain that it is dry (use a hairdryer, if necessary) and smear PVC glue around the edges. Sometimes that's all that it takes on a leaking plastic drain or vent pipe. There is no "pressure" of any kind on a vent pipe.
Good Luck!
Mike