Background: 36 year old single story stick built house on slab, the geniuses that built it forgot to provide a condensate drain thru slab for updraft central air unit in closet. They provided a cute little plastic sump pump that sits in the return air plenum under the unit, that directs the water, via 3/8" copper tubing, up into the attic, thence 10 feet over and down inside an interior wall behind the adjacent bathroom, where it pops out under the vanity/sink, then into a drain connection designed for the purpose of a dishwasher hook up. It's been trouble free other than having to clean the pump out every three years or so, and advising the occasional overnight guest not to worry about the frequent gurgling sound from the sink.

A leak has finally developed very close to where the copper pipe comes thru the wall and cabinet under the sink, as during a pumping cycle (that lasts about 4 or 5 seconds and pumps about a 1-1/2 cups water), I can see seepage running down the back cabinet wall. I suspect the pipe is kinked where they bent it to come thru the wall, and perhaps over the years, has finally eroded thru.

Tearing into the wall, whether under the sink, or on the opposite side (my bedroom) is what I'd like to avoid, and I thought of a simple fix. The pump itself is designed to accept a 1/2" clear vinyl hose, (of which I've got about 3 feet of installed, presumably to provide for flexible placement of pump). The 3/8" copper tube fits snuggly into the other end of the hose, with a hose clamp. I thought I'd cut the copper tube right above the A/C where it pops into the attic, and get some new 1/2" vinyl tubing and run it over about 12 feet to the vent stack for the bathroom drains, bore a 3/4" or 7/8" hole into the PVC vent pipe as close to the attic floor as I can to minimize increasing the head on the pump, and shoving the hose for several inches, pointing down into the pipe, then slathering some silicon around it to keep rain water from seeping thru. I don't know the i.d. of the vent pipe, but I assume it's sufficient to allow adequate ventilation during, say a toilet flush, that the intrusive vinyl hose won't matter. And in fact, I don't know why the builders didn't do it this way to begin with, by using a Y connection on the stack. So am I busting a code doing it this way? Can I do it without having to cut in an offset Y (or whatever you call it) ?

 

Update: The vent stack is 3" ID. This single stack is apparently for the sink, toilet and bathtub. (Other bathroom has two 2" stacks, because the fixtures are on opposite walls).

 

Yes.... drilling into the vent would be against code. That is a dry vent.
The water in that pipe is all from the bathroom sink down.

 

Thanks PJ, in principle I can understand it being against code, but in practicality, the small amounts of water (1.5 cups a shot, about every half hour or so on a really hot day) shouldn't be of any consequence, I would think. And anyway, when we have a downpour, that goes into the stack, as none of the vent stacks have rain caps on them.

 

If it were to be proper..... it would need to be trapped at the vent line to keep the fumes out of the pump.

 

Yeah, I can see that could be a problem. Fortunately, in my case, the pump has a check valve to keep water from flowing back down the tube into the sump after it shuts off, and even if the valve leaked, the impeller intake is always under water in the sump, so the effect would be similar to a P trap.

 

So you're good to go.