positive pressure problem

[dschroder]

I just bought a house with all sorts of weirdness. Most fixtures go through a main sewer pipe with vent to attic.... Except for an upstairs bathtub and the kitchen sink/dishwasher. In the same upstairs bathroom, the sink and toilet drain with the rest of the house, only inches away from the tub.


The problem, when tub drains, kitchen sink gurgles. I thought I could just install a cheater vent under the sink. To test it, I unscrewed a cleanout located under the sink. After jerryrigging the cheater vent, no results. I then noticed that air was blowing OUT the drain, not being sucked in.

I don't quite understand the physics, but what are my options. I don't think I could easily reroute either of the drains. Nor would running a new vent stack be particularly attractive.

attached pic of wonky drain... the slanted pipe goes to kitchen, straight goes up to tub. why would a constant drain from tub push air up the other pipe? Can install a valve or something? Would putting a cheater valve on the tub help?

 

[Mr_David]

What is that hub? is your tub tile with w tile base and that's the actualt drain fitting for the tub? where's the trap?

That is odd

 

[dschroder]

Not sure, I think that is just a fitting. The tub is on the second floor, it has a trap under the tub, but I can't really access it without taking a ceiling down.

The junction pictured is in the basement where the kitchen drain meets the tub drain. It then goes under the cement floor, and presumably meets with the sewer line.

My brother-in-law thinks that the drain from the tub is a larger diameter, and when it meet the pictured copper pipe junction, it's causing a backup of sorts. The drain is a little slow, though not terrible. I already snaked the portion on the basement floor, and seems clear. I'm tempted to run a vent line from the where the picture pipe meets the floor across the basement and run it into the vent stack. I'm guessing affixing a big rubber bladder to the clearout wouldn't meet code.

 

[dschroder]

Option two... the steel pipe right next to the Y in the picture is an old unused oil fill line. I could cap it at the oil tank run a vent into it, and run a aluminum gutter from the old intake up the side of the house. I'm not comfortable with cutting steel though.

 

[Mr_David]

Option two... the steel pipe right next to the Y in the picture is an old unused oil fill line. I could cap it at the oil tank run a vent into it, and run a aluminum gutter from the old intake up the side of the house. I'm not comfortable with cutting steel though.

You don't want to do that. Doesn't sound like a good idea.

Drains never reduce in size down stream.
Do you think the drain stack in wall is cast iron?
That maybe the transition. inside diameter is the same.
maybe they used cast in the wall for noise reduction.

If the kitchen drain is slow and is not vented, this is probably wwhat is happening.
An AAV let's air in to break the syphon when a fixture is draining. But is one way. Does not let air out
The stack below the wye is backing up when tub is drained.
NO vent so as the water rises in the stack the air is trapped and builds up pressure as the water rises causing the kitchen to burp/gurgle.
You need a good thorough cleaning of the kitchen line to the main.

 

[plumbinggroup]

You must call the company asks for a cross-check: if the problem is generating because of complication at their end. In case, you think there is an obstruction in plumbing or shortage of gas.