I posted previously about a septic smell in the house And got some answers. My kitchen sink (1.5”) runs a total of about 15’ before it ties in with the drain for my washing machine. After the tie in it continues for another 25’ to a 3” drain that dumps into a septic tank. Because the washer is in the basement I had to install a pump to pump the water up and out to where I mentioned it ties into the kitchen drain. The new pump is quite strong and I get water backing up the 15’ into the kitchen sink. Is there a backflow valve for 1.5” PVC that I can glue in line to stop the water backing up and this is on a vertical drain line. The other problem is this entire line is behind a finished wall and ceiling where I have had to cut a hole into with approximately 2’ of the drain exposed. WHEW!