I have searched this board looking for an answer and the main solution is to snake the drain which I have done all the way to the main.
Here is the situation.
Washer sits on exterior wall 7ft from main line there is a 1 1/2" stand pipe 3 ft long that sticks out above the washer by 3 inches it 90 degrees into a 2" about 8 inches from floor the 2" pipe then connects to an Iron pipe that goes under the floor over to the main. When washer is pumping out it overflows the 1 1/2" standpipe. I have thought about converting the stand pipe to a 2 inch pipe as well but am unsure if I can make the connections as there is not much room for error with the 2" pipe in the wall. The 2" pipe also serves the kitchen sink as well as dishwasher. Everything points to a vent issue however everything else drains correctly. My question is this if I remove the clean-out that is further up the 2" pipe below the upstairs sink and dishwasher and attach a 90 degree up and a 2 " pipe for an extra vent will this solve the problem with the washer or cause another issue with gas. History: when I moved in one of the joints in the 2" pipe was not cemented in so there was an extra spot for air to vent into the system which caused a slight drip when the upstairs sink and dishwasher were used I repaired that by cementing the PVC together and that is when my current problem occurred. Any help would be appreciated.