Primer is certainly something to consider.
I've had too many joints fail, especially on the larger pipe. Oddly enough, the type of glue used, and the weather, seemd to be the biggest factors.
The 'electrical' glue is pretty thin; add a hot sun and lower air pressures at altitude, and you have a prescription for the stuff to dry much quicker than you can assemble the pieces.
Oddly enough, some of the 'plumbing' stuff - like the gray glue - has a heavier body and allows for a longer working time. Using primer also seems to aid the working time. The PVC 'cleaner' they sell (clear rather than purple) seems to extend working time as well. The 'cleaner' is nowhere near as aggressive a solvent as the primer.
I note that the plumbing code requires the use of primer. Naturally, we are not concerned about any 'leaks' in our pipe; it's the wire insulation that keeps the electricity inside.
