Ok. We have a septic tank in case that’s important. the kitchen sink recently started backing up. I dumped a ton of drain cleaner down there. Just about every brand and type there is. Even thought it might be dead bacteria in the tank so dumped septic shock last and waited a day or two but still no change. I snaked the drain as best I could but eventually hit a bend that I could not get past. You can hear the snake hitting on the joint. So I noticed there is an air admittance valve. Bought a cheap one to replace. Still backing up so I bought an expensive one. Still backing up. if I remove the valve the drain works better but only to a point. If I throw too much water at one time like a load of laundry or dish washer it will overflow at the point where the valve SHOUKD BE. If I only use the sink at half flow I can use it without issues (except for not having the valve.)

so I finally got around to testing my dwv system. im hoping to do a rough in inspection with the town in the next week or so. anyway, I was going the water testing route. i plugged all the drains and the toilet. Went up to the roof with the hose and started filling the system with water. The system is pvc for the most part things seemed ok, but the water level did sink over time. I went down and inspected everything, but didn’t see any leaky joints. I was thinking some air will exit the system, and as it bubbles up it would reduce the water level, but how long does one wait and how much air can one expect to escape the system. i can see why the air testing method might be preferred, but am Leary with the pvc.