Toilet “Exploding” - Positive Pressure Issue?

[BritGarnell]

Hi Everyone!

Hope you are all well and had a good holiday! We have an issue that occurred over the holiday that I “think” I might be on to but all and any guidance would be super appreciated!

So long story short, we had a new bathroom added where there was not one before on our top (second) floor. The stack for that new bathroom runs straight down the house, turns horizontally in the basement, and then joins original main stack in the basement. I know for a fact that the new stack does not penetrate the roof - they just used an AAV.

We didn’t know we had any issue until we’ve had family staying for the holidays and using the spare bedroom and bathroom down in the basement. That bathroom is below grade so flows into an ejector sump.

Whenever that basement bathroom is used, air occasionally pushes out of the toilet in the new upstairs bathroom pretty violently - shooting water everywhere (of course keeping seat down now!).

So my working assumption is when the ejector pump fires it’s pushing air into the new stack for the new bathroom that then has nowhere to go but out of the new toilet.

Does this sounds reasonable? I’ve attached some picture that shows the ejector line does look to be plumbed directionally correct (flowing right way) - but air could be traveling other direction? Maybe because of the force behind it?

If so, is there a solution that could happen in the basement vs opening up walls in the new bathroom?

I’m thinking add a vent on the horizontal portion of the new stack after the ejector pump that ties back into main stack? Or would a back flow preventer in same place work? Or maybe tie ejector directly into main stack?

In the pictures, the horizontal line that the ejector pump runs into is also the new stack that runs up to new bathroom.

Thanks so much!!!

 

[BritGarnell]

I had an idea! I've opened that clean out on the horizontal line behind where the ejector connects. Thinking if ejector is pushing air the wrong way up that line it will escape there and I shouldn't get any problems with the upstairs toilet! Does that make any sense to anyone?

If it works will obviously close that back up (sewar gases!) but thinking then I can add a vent line there that runs over to connect to the original main stack a couple of feet away...any thoughts anyone?

 

[Sponsor]

 

[BritGarnell]

Well that didn't solve the problem but sort of did...opened it up and we have water! So I think I have a regular old main line blockage! Of course, had already checked for that previously but maybe not quick enough so water had drained. Out comes the snake!

 

[Reach4]

So my working assumption is when the ejector pump fires it’s pushing air into the new stack for the new bathroom that then has nowhere to go but out of the new toilet.

Does this sounds reasonable?

Not sure, but the pipe being pumped into is vented with a roof vent, right? So if pumping water into the system, there should not be significant pressure. Also the pit the pump is pumping from is supposed to be vented with a real vent, not an AAV. Is it vented with a real vent? That would not cause the second story geyser. Clogged pipes can.

Well that didn't solve the problem but sort of did...opened it up and we have water! So I think I have a regular old main line blockage! Of course, had already checked for that previously but maybe not quick enough so water had drained. Out comes the snake!

THat is a big pipe. Consider getting a drain cleaning pro with the big dangerous snake.

Sewer or septic?

 

[Sylvan]

This is why I never, ever considered using a cheater vent