I finally got around to drilling some of my 10g tanks for a continuous overflow system.
Now I have a few questions.
Should I use standard PVC solvent/glue to assemble the PVC pipe into the bulkheads? Will this be toxic to the animals after it dries?
If not, what should I use?
Or should I only glue the PVC on the outside of the tank and only use plumber tape on the inside fittings?
PVC cement is fine for fish, plants, and other aquatic organisms after it sets up. I also allow the plumbing to air out for a day or so, then run water from the garden hose through it for a few minutes before installing it in the tank.
For structures that stay totally inside the tank I do not use glue at all, just push together slip fittings. Structures that are outside or both inside and outside the tank do get glued. Using threaded fittings and Teflon tape works just fine, too. But then you need to glue on the male and female adapters anyway, so you are not really getting away from the glue.
I also paint the visible portions with Krylon spray paint for plastic. Flat black hides the pipe the best.
I finally went out and got all the parts I needed. I decided to only glue the pieces that were in contact to the bulkhead and the horizontal pieces on the outside. I only plan on using these as slow drains, e.g. ~5 gallons per hour.
Need help on assembling bulkhead overflow 
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