Phil, just use weldon 16. It will glue all kinds of crosslinked plastics: PVC; acrylic; polycarbonate; and just about any of the more commonly available plastics. I got it at a local plastic place, most hardware stores do not carry it. You can use weldon 40 but it is a two part type glue, it is for really high end precision work where appearance is the key. At least for what I'm doing, I don't care about much but strength and watertight!!!
The weldon 16 comes in a 5oz tube and is really easy to use. The 5oz has enough glue for a couple of dozen aquarium setups including sumps, refugiums, overflows, it does not take much!!! I have a feeling the tube I bought ($5), will last a long time. [smiley=biglaugh.gif]
I just glued about half of my skimmer together and it was dead simple!! [smiley=thumbs_up.gif]
Acrylic Tubing 
&&&&For he today that sheds his blood with me shall be my brother.&&&&William Shakespeare
80 gal plywood/glass reef tank, AquaC Urchin Pro w/Mag 3, 38gal Sump/refugium w/Mag9.5, 2 Maxi Jet 1200, 2-200 watt Hagen Heaters, 100lbs CaribSea Aragonite, 80lbs handmade Aragocrete rock, 2-110W 48" VHO Actinic Blue, 2-110W 48" VHO 50/50, RO/DI, DIY coiled denitrator, Bi-color Blenny, Damsel, Yellow Tang, red/green lobophyllia, zooanthid frag, cabbage coral, asst. mushrooms, toadstool leather, frogspawn 
