ABS pipes in 72 rear bumper

[mello mike]

One of my next projects is to drop the pan and cleanout the debris and rust proof the metal brackets and frame in the rear bumper.

Part of this effort will be to replace the ABS pipes in the rear bumper, right now they leak and that's the main reason why I have rust in the rear. This looks pretty straightforward but I do have a couple questions. How is the black water tank connection made? Is this typically a screw fitting or attached with a clamp? It also looks like the 1 1/2 inch ABS connects to a 3 inch ABS as part of the drain. I haven't seen a coupler like this at HD or Lowes. (see pics).