I am helping my son work on an old house he recently purchased. I have done plenty of plumbing, but this is the first time I have run into this. In his powder room, he will be installing a pedestal sink (I hate them, but it is what his wife wants). The existing PVC drain line in the basement under this powder room is 1 1/2". All 1st floor plumbing was completely demo-ed before we got there. The pedestal sink, I assume, will require a 1 1/4" tailpiece and strainer, and an 1 1/4" trap. Where do I transition to 1 1/2"? I am thinking the best place would be at the trap adapter, but I would like confirmation. Would it be better to transition after the tailpiece and use an 1 1/2" trap? Thanks in advance.