A friend of my wife's has had a recurring problem with the waste through her kitchen wall blocking. It takes waste from dishwasher, waste disposal unit and washing machine. If it was mine I would have investigated it and made sure there are no burrs on the pipe, etc. But every time it happens she calls a plumber who merely unblocks it.
I was wondering if there is an elbow which has a screw cap that can he removed for unblocking. She would then be able to do it herself. I used to see them in metal but are they available in plastic 32mm? If so I will get her to ask her plumber to fit one (I may even do it for her)