How to cleanout a clogged vent stack?

July 22, 2008 5:42 AM

Help me best attack a clogged vent stack.

I've been in my late '30s house now for two years and the two bathroom vanities (located one on top of each other) have always drained slowly. I've cleaned out the traps and snaked periodically and that has always helped somewhat but never to the point that I could truly claim victory.

I've finally gotten around to going up on the roof to peer into the vent stack openings (I have three of them and they are all fairly large (3.5" diameter pipe). None of these pipes are covered or screened which seems like an oversight to me. I do have very large trees in front and rear of the house so who know how much stuff is down there.

Anyways, two of the the three pipes are clear. In the not clear pipe, I can see standing water. Using a manual snake, I can make it down about 11 feet before I hit an obstruction (or a piece of pipe that I can't navigate). Of that, about 7 feet of it is standing water.

I tried the snake for some time, but clearly I was unsuccessful. Besides calling a professional with a professional snake, is there anything else I can try? I've thought of trying the garden house with a straight line high pressure nozzle but haven't bought one yet. Is there any safe enzymes or bacteria that I can put down the vent stack that eat away at the (presumed) organic material that is blocking my vent? I do have a shop vac but due to roof design it would be tough and dangerous to get that up there.

Thanks in advance for all your suggestions.

posted by mmascolino to home & garden (11 comments total)

What kind of snake have you got? A flat tape-type snake ought to get around any corners.
But first, stick a garden hose in there, with a high-pressure nozzle on it (not the pistol kind, but the straight kind). Root around for a while, and the obstruction should get flushed down. If it's leaves, they've probably halfway decomposed so they'll break up and flush down the drain, and won't create a new clog lower down.
posted by beagle at 5:54 AM on July 22

Sorry, I should have noticed you thought of the hose idea. I endorse it.
posted by beagle at 5:55 AM on July 22

See also the anonymous comment at the end of this thread. They're talking about a bulbous attachment for the end of your garden hose, essentially a seal around the end of it, so that when you turn the water on, you're creating a lot of downward pressure into the vent. Inquire at a hardware operation with knowledgeable counter guys (ie., not the large orange variety).
posted by beagle at 6:01 AM on July 22

With vents of that large a diameter, you can imagine small animals or even small solid objects like twigs or perhaps pine cones becoming the base of a clog. You can rent 50 foot or longer power snakes from many Home Depot or Lowe's home centers.
posted by paulsc at 6:01 AM on July 22

There's nothing wrong with the do-it-yourself approach, but at some point you might be better off spending 200 bucks and getting a sewer router pro who has all the right equipment, solves these kinds of problems a dozen times a day, has seen it all and will be finished in 30 minutes.
posted by JackFlash at 7:45 AM on July 22

N'thing the garden hose. We just pushed it in and let it run to clear a blockage a few years ago. My parents haven't had a problem since.

Although it is very conceivable the blockage is more serious than a hose can solve.
posted by pixlboi at 7:59 AM on July 22

I had the same problem, and bashed it through in 10 seconds with a 20' long piece of bamboo.

3.5" seems crazy big for a vent stack. Are you 100% sure that's what it is?
posted by Patapsco Mike at 8:33 AM on July 22

Thanks all for the suggestions. We are going to try the garden hose approach here in a little bit after we fabricate some proper coverings out of wire mesh and some hose clamps.

And yeah, I am shocked too on how big these pipes are for the purpose but they are indeed vent stacks. The bamboo however is a good idea.
posted by mmascolino at 9:31 AM on July 22

Also, if the obstruction you are hitting is actually a bend in the pipe, it's conceivable that there is a horizontal section (not really a good idea in a vent, but sometimes unavoidable), and that that section has sagged somehow so that water is actually trapped in it. You could clear that out but eventually rain would refill it. You'll know, though, when you break through the clog. The water should then drain entirely on its own, and the sinks should empty smoothly. If not, water might be pooling in a sagged section, and you'd have to get that re-leveled. Twists and turns in the vent might be why they used 3.5" in the first place.
posted by beagle at 9:35 AM on July 22

3.5" seems crazy big for a vent stack. Are you 100% sure that's what it is?

In most jurisdictions that have freezing weather, a 4-inch stack is required where it goes through the roof. This is to reduce the possibility of the stack closing due to freezing water vapor. The stack may be smaller diameter inside the house.
posted by JackFlash at 10:42 AM on July 22

By the way, this is a reason to carefully consider your plan to put screens over your vent openings. In cold weather your vent screen could easily freeze up from moisture or be covered by snow.
posted by JackFlash at 3:04 PM on July 22