I am redoing the piping under the kitchen sink. The P trap horizontal pipe 1.5in extends about 3 to 4 inches into the horizontal sewer ABS 2in pipe. Should I trim the P trap pipe to be closer to where the two meet? Or is it better to keep it long? [attach]101322[/attach]

Hi everyone, I continue To uncover/fret about some of the mysteries in our home. One of our basement bedrooms has a walk in closet. Within the closet is a large panel which allow access to the main plumbing stack for the house. One wall of the closet is shared with the bathroom next door which has sink, toilet and shower. The house has no basement floor drain. As a result, the shower and toilet were constructed on a raised floor....presumably to allow for their drains and proper flow to the main stack. The closet has 2 valves sticking out of the wall, right along the part of the wall where the shower is. I assume these valves are shut offs for the shower. (All of the valves in the house are stuck in the open position. I’m afraid to force them closed for testing, for fear the stems will break. Finally, the closet has an exposed (through a small opening) saddle valve. For the life of me , I can’t figure out what it controls. It too is stuck...not sure if in the open or closed position. No ice maker piping is found in the basement kitchen. No furnace humidifier. There is a sump pump in the same bedroom...located in another “closet”. What else should a saddle valve typically control? Any thoughts on how to figure it out, or should I just forget about it?