The washing machine in this house has a dedicated drain pipe that connects in after the trap for the laundry room sink. Every time you use a lot of water at once or you drain the washer the water will start coming up through the drain in the sink and slowly drain out again. I already cleaned the pipe from the washer to the trap and from the trap to the service opening that goes from the house to the sewer and it appears that between the house and the sewer there is a partial plug that's restricting water. I put a 25' drain snake down the service opening and I pulled up a bit of shit (literally) but it wasn't whatever is blocking the pipe. I can't fit a drain bladder in the pipe because it won't fit around the corner in the T-joint of the service opening and I'm optimistic any chemical cleaners will remove whatever is down there. I have already tried flushing the line with very hot water but that did not work either. Is it time to call in the pros?