pvc pipe repair

I have a PVC return line that is below the water level I need to re-plumb. Is there any way to "plug" the pipe so I can make the solvent welds?

Sure. They make all kinds of plugs. The two most common are the expanding cork and the screw-in kind. The Expanding Cork is a rubber cork that you jam in the return, after removing the fitting. There's a wing nut on it that to tighten to make the seal. The screw-in kind screws into the threads that hold the return fitting. I use these for my winterizing.

Cherne test balls & plugs are what plumbers use (I was a licensed master plumber for 25+ years). They are not cheap, but can reach into pipes where it's difficult to fit an end plug, and will seal even if the pipe is somewhat rough.

Oatey 240018 Cherne 1-1/2-Inch Test-Ball Plug
Cherne 270024 Test-Ball 2-Inch Plug

Cherne 270016 Test-Ball 1-1/4-Inch to 1-1/2-Inch Plug

Here's a typical small plug:

http://ecx.images-amazon.com/images/...sL._SY300_.jpg

But you'll need to look at the Cherne catalog using the product numbers, to be sure of what profile you're getting: http://www.cherneind.com/Pneumatic/Test_Ball/