When I install our new double sink during out kitchen remodel would it be permissible to put the main sink and the 2nd smaller sink with disposal on separate fixture arms with their own p-traps at different heights draining into the same 2 inch drain pipe? Due to the greater depth of the new sink the garbage disposal is going to sit much lower and does not look like it would drain properly with the current fixture arm height. Therefore, I was thinking of adding a separate run just for the disposal.

A related question: if I continue to use one p-trap with the standard merge type joint, should the fixture arm size be 1-1/2 or 2 inch for a large double sink? The current fixture arm size is 1-1/2 for a much smaller double sink.

I want to do something similar, but use two separate fixture arms (drain lines) at different heights that will merge into one common vertical drain further downstream in the wall.

We are having problems, too, with our outflow from the garbage disposal. Is this the type of problem you are anticipating? Here is our set-up and why I am very interested in the answers to your questions, too.

The reason that it does not pass under UPC is simple:

UPC-1001.1 only one rap permitted on a trap arm.

Under the UPC you could install a second trap arm in the manner you propose, however if you do so you must compute the load at 3dfu for each trap. Given that the UPC limits a 2" branch line to 6dfu's you may not have any other fixture attached to that line.

The simple solution is to begin by removing and discarding the factory supplied 1/4 bend on the disposal. You then get a "Disposal Type End Waste Kit" which will have a straight cross tube with a flanged end. The flanged end is attached directly to the disposal body where the factory supplied 1/4 bend is now. This will give you a horizontal cross tube at the same elevation as the disposal discharge port, approximately 4" higher than the current cross tube.

Attach the code required "Baffled Tee" to the end of the cross tube and the tailpiece from the second sink. The P-trap is then attached to the discharge end of the Baffled Tee. (See Attached Illustration.

Previously it was mentioned that the pipe should be black. That is not correct. The IRC & UPC both approve schedule 40 PVC (White Pipe) or ABS pipe (black pipe).

The slip joint type fittings I.E. End waste kit & P-trap are generally made of polyethylene or polypropelene and either type are fine.

The plastic is so thick that it creates a real clog point, especially on the output of a GD.

More than have the pipe bore is obstructed.

Metal baffle Ts have less blockage in the line.

I'd run the sink and disposal into a double wye and then into a p-trap, but that's not legal because there isn't any separation between the two where they meet. That's why I was thinking of separate fixture arms.

That statement is totally incorrect. You could in fact vent the entire bathroom group with one vent.