Q:

What fittings can I use to re-route my copper DWV pipe?

I need to change the direction 90 degrees and then transition from 1-1/4" copper to ABS. This is a dry vent that I am trying to reroute.
How can I reroute the vent as shown in this picture? It will go between the 3" soil stack and that vent that has some white drywall spots on it. (The line is drawn in front of it but it'll go behind.)
All the horizontal wood you see in the picture under the joists is gone--that was the framing for the wall that was hiding these pipes. I removed that to make room for this pipe's new route. I need to stay on copper till I pass through that narrow space, after that I will switch to ABS.
So it will be the original vertical pipe, then a flexible elbow, then a short horizontal copper run and then the flex connector you posted below and then ABS.

Here is the challenge, top view of a horizontal cross cut at the bottom of the joist level.The pipe will have to go along the long thin arrow in the sketch toward the wall

A:

I'm not sure why you need a flexible elbow. I'd use a 45 above the plates (near the insulation), bringing the pipe out of the wall plane, then a 90 to go right underneath the joists. Isn't it that simple?

If you find that the fittings are too long for that, use two 45s on the vertical pipe, one out and one back to vertical, but offset to the left (near the 22" mark on your tape measure) so you end up tight with the wall plate (or its former position). Then a 90 gets you exactly where you want to be.

In all cases be sure to leave a small gap to the wood to avoid expansion ticking when you drain hot water. Cut and dry-fit all parts, then mark them as to position before disassembly.

