Water flows up vent stack, rather than out waste pipe (kitchen sink)

[jbrukardt]

I have the strangest problem. Water is willfully ignoring the path of least resistance, and rising up almost 12 inches to flow out a vent stack cleanout instead of down the drain.

Long story short, my kitchen sink has a brand new drain pipe (1.5 inch pvc) that i put in myself about a year ago. The pipe goes straight from the kitchen sink, about 4-5 feet to a wye, that goes up vertically 12 inches, then over 12 inches, then up 25 feet for a dedicated vent stack. continuing on past the wye, the main drain line goes straight for about 20 feet, with a 2 or more inch drop every 10 feet (great slope), until it makes a soft 90 degree turn and shortly goes into the main stack.

Zero water is reaching the main stack. Or the latter 90% of the drain pipe. Water flows down the sink, backs up very shortly, rises UP 24 inches into the vent stack, and only releases pressure when the cleanout plug is removed. If you run the kitchen sink with the cleanout removed, all the water from the sink flows out the vent stack. i measured.

Potential issues

1) grading issue

Nope, the slope of the drain pipe is severe, more than it needs to be

2) Clog (the most obvious)

The entire drain pipe is less than 1 year old, and i have tried everything known to man to unclog it except cut it out entirely and replace the entire pipe. Drano, bladder, snake, boiling water, pressure from a shopvac, suction from a shopvac.

3) Some weird negative pressure from the vent stack "sucking" the water up?

Never heard of this in my life, and when i had the pipe chopped up to replace the wye yesterday, i was getting a cool breeze out of the vent stack.


Things ive tried:

Replaced the whole wye and vent stack
poured boiling water down the pipe and felt the pipe to see where the water stopped (it stops less than 6 inches after the wye)
Regraded the whole drain (it currently was about an inch every 10 feet which should have been fine, i made it 2)


Diagrams and pictures:

Did i mention all this is in a 16 inch tall crawlspace?

Its terrible under there. Dont make me go back under there.


In all seriousness though, i can say with absolute certainty that the vent stack is not clogged (its brand new) and with fair certainty the pipe is not clogged.

That leaves me with two options

1) a squirrel crawled through the damn cleanout when i left it open for a bit and died in there, creating a complete blockage

2) someone snuck into my house and poured a gallon of epoxy down the pipe

3) i have a major backup from my septic ( other drains in the house work fine, all second story though, this is the only first story drain)

4) Water ghosts.

 

[jbrukardt]

A = no, no water coming out of the cleanout when the upstairs shower, sink, or toilet are run.

I am about due for a septic cleanout, its been about 5 years in a single person household.

 

[Sponsor]

 

[jbrukardt]

although one of the tests i did would seem to contraindicate the septic issue. I put a shopvac on the drain, and it sucks whatever water i put in out (measured), but no more, and no less. And no sewery seeming water. I put clean water in, i get clean water out.

 

[jbrukardt]

also, nothing came gushing out the pipe when i cut it away and replaced the wye.

 

[Terry]

You have used water pressure 90's on the bends. That prevents you from snaking the line, and I'm surprised it worked as long as it did.
When you installed a new drain line, it should have been done with drainage fittings.
Horizontal fittings are long sweeps.
Going from horizontal to vertical can be a medium 90
Going from vertical to horizontal needs to be a long turn or wye fitting.

You should go down there and remove the right angle 90 that is only used for water supplies, not drains.

 

[jbrukardt]

ok, thats good advice. Thank you. All those are right by the drain and fairly easily replaced. but thats not where the clog is. The one turn way way down another 30 feet by the main sewer stack is a long sweep, so im good down there. Theres only one water pressure 90 in the whole thing, which is right under the drain

edit: one on the drain stack as well i guess, but in normal conditions that should never see anything but air.

 

[hj]

Your water is NOT rising 24", it is draining from a sink at least 12" higher than that. In order to defy the laws of physics and gravity, the cleanout would have to be ABOVE the level of the sink. According to your drawing you have an unvented sink drain. The "vent" you show is strictly cosmetic and does absolutely NOTHING functional. You have a plugged drain line and need a better snake to clear it.

 

[jbrukardt]

Your water is NOT rising 24", it is draining from a sink at least 12" higher than that. In order to defy the laws of physics and gravity, the cleanout would have to be ABOVE the level of the sink. According to your drawing you have an unvented sink drain. The "vent" you show is strictly cosmetic and does absolutely NOTHING functional. You have a plugged drain line and need a better snake to clear it.

How exactly is it unvented?

 

[Terry]

How exactly is it unvented?

The vent needs to be above the trap arm that the p-trap is on. You have your vent coming off the basement line.

This picture shows a vent at the correct location.
The vent doesn't go horizontal until it's 6" above the "flood level" counter top.

 

[jbrukardt]

Thank you Terry,

Unfortunately the way the house is built, drilling a hole above or in line with the p trap would put the exit right into an oil tank. I just copied the existing design when i replaced the piping (often not a wise thing to do), and by my very brief research, it looks like that design is intended for more of a waste pipe as per this picture

ht

While certainly not correct, it should still be a functioning vent?

Either way, my issue isnt relating to the vent to the best of my knowledge.

 

[Terry]

This drawing you posted looks nice.

For whatever reason, your piping isn't draining. Normally drains have fittings that allow for snaking to clear them. Have you got that thing draining yet?

 

[jbrukardt]

Just got back in town to work on it again. That pressure 90 you said to replace will be coming out, and I can try to snake it from there as a a straight shot. The vent its very similar to how the toilet vent is set up in that picture. It doesn't go into a more complex stack though. Just goes straight to the roof, it's own stack

 

[hj]

quote; my issue isnt relating to the vent to the best of my knowledge.

What "knowledge" is that? According to your drawing and description, it has EVERYTHING to do with it, Under certain conditions the sink might drain if the vent were proper, but not the way it is now. The drain being plugged is the major problem.

 

[HomeownerJ]

Hi there, did you ever figure this out? Ran in to a similar issue where sink water seems to be draining up 24 inches, left 3 feet and down the side of my vent stack. Oddly enough my sink isn’t backing up with water. Posted something last night about it and just found this post. Some good advice here - particularly regarding the 90’s.