Bob(not a plumber)
New Member
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.