Basement toilet splashes when upstairs dishwasher or clothes washer are draining

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Bob(not a plumber)

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I finished my basement last year and added a bathroom below the kitchen and laundry. I wish I could draw this but I will try to explain. The 2 1/2" drain pipe from above comes down into the bathroom in a corner. The toilet and tub are upstream to where the drain takes a turn under the floor to the main stack, 40 feet away. The bathtub is farthest away (5 ft.) and is vented with an AAV, which is sealed inside the wall. I know, I've just found out that is not right. The toilet is between the bath tub and the upstairs drain. The sink ties in 2 feet downstream of the corner and is also vented by an AAV inside the wall. I have asked 2 different plumbers about this problem and both said to first try snaking the drains for clogs, but I know there are none. The problem has been there since it was installed. The drain under the concrete slab to the main stack was replaced with 3 inch, as it was originally only 2 1/2 inch. All of the plumbing is new. If I fill the kitchen sink and laundry tub both up and let them drain at the same time (the most water I can drain for a simulation) it doesn't splash. It only happens when waste is being pumped in. The fixtures in the basement otherwise work fine. Could it be that the vents are not allowing enough air because they are sealed in the wall? That doesn't seen reasonable to me (not a plumber) because wouldn’t the draining water from upstairs be pushing back to the toilet so an AAV wouldn't let that pressure escape anyways? Or is there so much suction happening to draw air into the toilet to make it gurgle as it sucks in air and cause the splashing? I'm sure I'll get a few different opinions on this one, so let them fly. Thanks in advance for helping me solve this.
 

Cacher_Chick

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Sounds to me that the toilet is unvented and the pressure from upstairs is making it's way there.

An AAV is not made to vent pressure, it only allows air IN to prevent a trap from siphoning.
 

Jadnashua

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Also, consider that any pipe that is a drain cannot be (with few exceptions) be used as a vent for anything below that drain. So, essentially, when all that water rushes down the pipe, there's nowhere for the air to go because there are no vents in the basement. As mentioned, an AAV only lets air IN, not out, so when the pipes are pressurized by the drains, especially when pumped, any trapped air has to go somewhere, and it's bubbling out at the weakest point.
 

Bob(not a plumber)

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The air has a 3 inch pipe to travel down to the 3 inch vented main stack. I'm sure this pipe is never full enough to cause back pressure, especially if the pipe feeding it is only 2 1/2 inch. Unless of course it is blocked partially, hence the two plumbers suggestion to snake it. If it isn't blocked, and this is really what is happening, how do I fix it? Any other ideas out there??????
 

Nukeman

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If the AAVs were not buried, I would say remove one and test again. AAVs don't work well for pumped flows (like a washer) as they can only let air in and not out. You could pull the p-trap from the lav and try this test instead. Whether it would act like a proper vent for the toilet depends on the arrangement of the plumbing.

The best thing to do would be to make a drawing or posts some pictures (if you have some) on how the plumbing is currently laid out. That way, we can see if there is maybe a problem with the layout or if it might be a partial blockage. Since the problem started when you 1st installed this plumbing, one would think that the problem is with the layout. However, since this bathroom didn't exist before, the problem (say a partial clog) could have been there and it just wasn't noticed (I assume there were no other fixtures in the basement prior to this bathroom install).
 

Terry

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This is why plumbers and the plumbing code prefers real vents.
Then you know that using one fixture will not affect the others,
You will need to open walls up and ventilate your AAV's and see if that helps.
You can use grills to cover the holes.
If it's on the outside wall, and the inside is tiled, maybe you can outside grill it. Getting ugly.

In the picture below, you can see how the lower vents tie in.
In remodels, I've found plumbing in the next floor and tied into that. Yes you wind up cutting walls, but the plumbing works when you are done.
Otherwise, why bother?

dwv_b2.jpg
 

Bob(not a plumber)

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nukeman, that is a great idea, remove the trap and test, thank you. The history of the basement is, the builder decided on his own accord, to relocate the original basemennt plumbing to a convenient spot right next to the main stack. This totally screwed up the basement floor plan so I had the plumbing put back to the original planned location. This was done after the upstairs was finished and a proper vent could not be added without major destruction to the kitchen. The plumber I hired to do this suggested the AAVs. Another plumber was going to incorporate a wet vent loop instead. Not sure if I choose the right plumber here. Maybe both ideas were bad. I cut up the concrete and replaced the drain back to the stack with 3" pipe and removed all of the original rough in plumbing for the other bathroom. The only other basement fixture is the hot water tank. I've drawn a picture of the layout, I hope it shows up in the post here. I suppose I could have ran a vent along the ceiling all of the way across the house to the vent that was provided for the original rough in. How far can you run a vent vertically and how much slope does it need?Drawing1..jpg
 

Nukeman

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If I understand correctly, the 2.5" line and this bathroom connect together and flow (in 3") and then connect to another stack which then flows to the city sewer. Is that correct (waste flows towards the right on your drawing)?

How did you tie your lines together in that corner? Is the toilet also on a 3" line? Were the pipes installed with proper pitch (1/4" per foot)?

For a vent, you really can have them just about flat (above the flood rim+6"). A vent will work in any direction (up, down, sideways), but inspectors like to see a slight grade back towards the drain so that condensation and rain water can drain (but the slope can be minimal). It sounds like you could have run a real vent across the basement and tied into the original rough-in vent, but is hard to know for sure without seeing it.
 

Bob(not a plumber)

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Terry, I can cut drywall and put grills on the holes if you think that will help. The one for the bathtub can be accessed through an 8 inch section of wall we made to incorporate the plumbing and the sink can be accessed through the back of my sons closet. I think that removing the sink p trap and testing may determine if this is going to help. I think maybe the one that will help the most may be the bathtup as it is upstream from the toilet. Do you think the toilet splashing is due to suction or backpressure? As far as running a proper vent upstairs, you are right, do it right or not at all. I was told this would work so I thought it was right. The only wall I could have gone up to run a vent already had all of the laundry and laundry tub plumping, dryer vent and wiring, stove wiring and vent, and central vacuum cleaner plumbing, there was just nowhere to put one. The other walls are concrete and the pipe would have to come through the floor. My plumbing arrangement doesn't seem to have any type of direct vent for the toilet. I guess this is the main problem. If opening up the AAvs to breathe doesn't work, what else can I do?
 

Bob(not a plumber)

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Yes nukeman, your assumtions are correct, the waste flows to the right in the drawing to the main stack and directly to the city sewer. I made sure the drain was sloped, I believe it was a 15 inch drop. In that corner, the 2 1/2 inch comes down in to 2 45 degree elbows into a 3 inch Y. The toilet is on 3 inch as well and runs to the corner with a 45 degree elbow conecting to the Y. I think the bath tub drain actually comes to a 1 1/2 x 3 inch Y that is between the toilet and the corner. It is buried under tile and concrete now. Yes, I think I could have run a vent across the basement to the original rough in vent, although there was some heating duct in the way. Could I have gone through ductwork with a horizontal vent pipe? My previous question should have been how far can you run a horizontal vent, not vertical, sorry.
 

Jadnashua

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The vent should be sloped back to the drain, and no, you shouldn't run it through a duct. It can run quite a long ways horizontal, as long as it is above the flood plane of the fixtures it is venting, and has some slope to drain condesation and rain water. You should avoid dips or U's, as they could eventually fill up with water, blocking them.
 

Bob(not a plumber)

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Just to clarify, I meant passing through a cold air return for about 3 feet, not running all the way down a duct. If the answer is still no, then I guess thats why we didn't do that! By the way, this doesn't sound like all that big of a problem until some one forgets to flush the toilet. Who doesn't flush a toilet!!!! ARRGGG
 

Nukeman

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When you pull the p-trap to do the test, you may want to put a bucket under where the lav line goes into the wall and also be able to talk to someone else who is near the washer during the test. If there is a partial clog after the lav connection, it will back up and try to find the easiest way out (which may be at the lav). If water starts going everywhere, you need to be able to have someone shut down the washer before your bucket floods.

The toilet does not really need a vent, but some locations require one (in my location, there just has to be a vent somewhere in the system to serve the toilet(s)).

I know what you mean about the challenges with running a vent when other floors above are finished. The original bathroom in my basement was not vented, so I tore up the concrete, replaced some pipe, and added vents. I was thinking of AAVs since they would be much easier (2-storey house + basement), but in the end I went with a real vent as I also had a laundry area down there. I didn't want to do all the work and then have the AAV not even work for the application. I'm glad I went with this route, but it was not easy and I still have some patchwork to do.
 

Bob(not a plumber)

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Ya, more good advice thanks, don't want any flooding.
I thought this project was difficult enough without thinking of vents. As my handle goes, I'm not a plumber. I had to make two 50 ft cuts in my concrete slab, brake it up, pack it out the basement to my truck, haul it away, dig a big trench, replace the smaller plumbing because this is the third toilet in the house, requires 3 inch, compact it and patch the concrete. By the time this was done, I left the rest of it to the plumbers to figure out. I didn't think the toilet really needed a vent, but most drawings show one. When I do this test, I will let you guys know what happened.
Thanks for all of the advice.
 

Bob(not a plumber)

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OK, thank you, that is most likely what we used then. I remember that the line had to be bigger due to a 3rd toilet, I may have been wrong about the size though, but I know we used what the code said, so if you are right, it is 4 inch. Which makes it even less likely that the line would be back pressuring, so I think it must be the vents starving for air. I'll be working on it this weekend.
 
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