Can I raise the height of a p trap arm?

If you mean shorten the sinks tailpiece- yes

TheEplumber said:

If you mean shorten the sinks tailpiece- yes

Click to expand...

Actually I'm putting in a p trap under the bathtub, no compression fitting on this one. Can't shorten the vertical (tailpiece) pipe. I'm wanting to raise up the 90 that connections to the U

nateo said:

Actually I'm putting in a p trap under the bathtub, no compression fitting on this one. Can't shorten the vertical (tailpiece) pipe. I'm wanting to raise up the 90 that connections to the U

Click to expand...

You can but it is not allowed by code. There is a maximum trap depth- I believe its 4" The reason for this is that a trap must be "self cleaning" Making it deeper allows solids to settle rather then flushing out while draining- or so I'm told...
Also, your 90 will determine the depth of the water seal- will it be higher then the base of your tub? If so, you'll always have standing water in your tub

Am I losing it? From that picture it looks like the tailpiece has to be extended so the back of the trap lines up with the T? I cant see anything wrong with that.

jagans said:

Am I losing it? From that picture it looks like the tailpiece has to be extended so the back of the trap lines up with the T? I cant see anything wrong with that.

Click to expand...

Yeh, you're losing it. He wants to do the opposite. In fact, as I understand it, he wants to make the adjustment at the trap by making it deeper

Looks to me he needs to add length to the tail piece to bring the trap down to the tee. Or move the tee up. Either one will work.