Transparent screw-on 6" cap for PVC pipe
Clear PVC does exist and you might be able to locate some from Commercial Industial Supply (for example).

With regard to gluing wire (insulation) to PVC, a copious amount of epoxy or silicone should work. Luckily, the pressure should not be extreme. The most important instruction is to drill the hole just large enough to slide the wire though without pinching or damaging the insulation. For the best result, the connection (wire in the hole) should be practically air tight before using glue. But glue won't last forever.

What tool does one use to open &amp; close these caps anyway?

Looks like you need a cleanout plug wrench or a Square for Counter-Sunk Clean-Out Plugs.

Edit- based on comment that a wrench could not be obtained-
Well, 2 inches is kind of large; perhaps a drum plug wrench is waht you need.



You just need to get anything (a hard piece of wood or metal) that is 2" x 2". But I think that a piece of plywood might be strong enough (birch would be preferable to pine). Cut a piece 2" x 2" (of course) and cut a nice long, wide handle. Pre-drill 4 holes in the corners of the 2" square before using screws (to avoid splitting the wood). Apply plenty of glue and screw the small square piece to the face of the handle. It might not work forever, but it will probably work a few times at least.