Sink drains slowly - no air behind water?

My kitchen sink has begun draining v-e-r-y slowly. I’ve cleaned the trap and found nothing. The dishwasher drains just fine, but of course the water is being pushed out by the internal pump. I’ve always understood that the drain needs an air vent in order to work properly. As Mike Holmes always says “need air behind water”.

In checking the PVC drain line I don’t see any vent. What I do see is a parallel PVC pipe that is connected at both end to my drain. Picture if you will a 20 foot run of PVC. Now picture a 10 foot piece of PVC next to it and tied in at both ends with several elbows. A closed loop.

Anyone have any idea what the hexk this is and if it is supposed to somehow help the draining process?

What you probably can’t see is behind the wall. There should be a vent pipe up through the roof. That’s where the air comes from.

Perhaps you have a clog farther down? Try a chemical drain opener or a snake.

I’m not really picturing it. You could just walk outside and look at your roof. You should see at least one 4 inch PVC pipe sticking out through your roof. That’s your vent stack (assuming it’s not your furnace exhaust). There may be more then one, but if you have one, at least you know the system is vented and the kitchen sink is probably tied back into the one, probably in the attic.

Your vent stack may be frozen, if this has just started in the last couple of weeks.

The vent stacks that penetrate the roof are for the bathrooms and are not connected to kitchen sink. The kitchen drain after the usual trap, goes straight down through the flooring into the cellar. In the cellar the PVC follows the floor joists over to the main trunk that goes into the septic tank. Trust me, there is no vent.

The only thing about the entire plumbing situation that’s odd is the extra PVC loop.

And that ‘main trunk’ should have a section that goes straight up through the roof. Each individual drain doesn’t need it’s own vent through the roof. For example, I have a kitchen sink, two bathroom sinks, two toilets, a shower, a floor drain and a basement sink but only one vent going through the roof.

My kitchen sink drain goes back through the wall, into the basement and connects to the main drain line, but also goes up to the attic to connect to the vent (which is the exact same pipe that the drain catches in the basement).

If you can get into your attic you might find some more pipes attached to some of those vent stacks. One of them may be from your kitchen sink.

If it drained well until recently, and you changed nothing in the plumbing sytstem, then it shouldn’t matter if the system vents normally or if it has some odd scalar energy perpetual motion feedback PVC loop. If none of that has changed from when the system worked, then that’s not the tree you need to be barking up and the problem is a clog down the line, or a dead squirrel in a vent stack.

I think you have a loop vent.
Often used for Island installation, but not always.

Sounds like your closed loop might be saturated with water due to a pin-hole air leak.

That used to happen with my Parent’s closed loop hot water heating. The pressure tank would fill with water, with the result that the expanded water due to heating had no where to go, except out the pressure relief valve.

Can you blow that line through to the septic tank?

If so, there is still a roof vent, it just may be harder to find and not directly over the sink.

If there’s a water trap between the loop and the vent stack, it’s of little value.

It’s not unknown for roofers to toss crap down the stack :eek:, or for birds/animals to block it with shit. :smack:

This is a real cellar, where you can see the whole system? * Only the kitchen sink is draining slowly? Are all your units on the same line into the septic tank?

  • (As opposed to a crawl space where you’re looking at it from one angle, with a flash light, kneeling in the mud, with your neck at a strange angle)

Did it work fine before?
I would assume the dishwasher is fine because it doesn’t use alot of water and drains quite slowly.

Is it PVC or ABS?

Can you take a picture or draw one? Is it a double sink? Where is the dishwasher connection?

The easy fix is to fill your sink and plunge it.
Remember to pull don’t push. A plunger is a suction cup not a battering ram. This is a common mistake, if you push the blockage past or into the air vent, you got bigger problems.

Liquid drain openers are a last resort. Beware, they are extremely corrosive and may damage pipes, especially plastic. Also, if it doesn’t work and you (or a plumber) need to open up the pipes, it can be a hazard.