Too bad those pipes are eternal. Usually in the elbow they are caulked. Before cutting, find out what type of transition you have in your sanitary house. Ideally, it is inside, but I do not know if sealant will look good. According to what they offer you can cut leaving about five centimeters to embocar a pipe with o´ring Greetings
I agree with Ricardo, those pipes are eternal! If you lose a joint, re-caulk with hemp and pitch and last another 100 years, if you have to transition between PVC and H ° F ° it is best to plug in a female union and caulk with putty Parsecs, prior thorough cleaning of the piece of iron; and do not use it for 24 hours at least to cure the putty inside