Rusty: Im strickly guessing but I have seen this several times before. If your house was once on a septic system before converting over to sewer, its entirely possible that 1 pipe went to septic tank while other pipe went to gray-water line. This was/is very commonly done on more expensive houses in my area even today. If house has always been on sewer obviously this theory will not hold water. If 2nd pipe is old gray-water line you could completely cap if off with no effects whatsoever.: House is over 40 years old, washing machine waste water is delivered to sewage via a drain pipe that has two vertical pipes made of the same material. One is shorter (we have the drain hose from washer inserted here) than the other. What is the taller one used for? Can it be capped with out messing anything up?