The toilet wouldn’t flush and would overflow insteading of heading down the 3″ pipe to the holding tank. I opened a 1 1/2″ tail end pipe on the end of the 3″ pipe to investigate and the toilet flushed great. It apparently either freed a vapor lock or allowed venting. I installed a vent cap on the 1 1/2″ pipe. Now a week later, the toilet is again not going down the 3″ main pipe again and is backing up and out the 1 1/2″ pipe and out the vent cap. !!?? I put a small pipe on the holding tank side to prevent pressure. Why would the water choose to go ‘uphill’? If I seal off the 1 1/2, the toilet goes back to not flushing. The main line looked very clear as I looked through the 1 1/2″ down the line after I first opened it. I’m thinking of adding an extension to the 1 1/2″ and making it go very high into the air because I assume the system is wanting venting? Thanks.
You are treating a symptom by opening the 1 1/2 inch pipe. There is a major problem, either the septic tank, if that is what you have, is full and you are getting an air lock, or the sewer system is obstructed with the same result. You will eventually reach a point with your 1 1/2″ solution where the pipe will be higher than the house plumbing and then it will overflow in the house.