basic questions

Answers:
1, I usually start the back flush as soon as I open the Black tank drain valve. I have a clear elbow at the end of the hose so you can tell when the black "stuff" is no longer flowing. Then leave the flush running until the water runs really clean. Stop the flusher, wait until all residual water stops and shut the black drain valve.

2. Not sure I under stand the question about lower light switch, but ALL wiring drops down from the top of the trailer. If you remove the existing switch, you should see the wires from above - add as much as you need and relocate the switch lower (you'll have to patch or cover the hole).

3 the simplest compartment light is a battery powered closet light from Walmart. Usually they stick up, or use a couple of screws.

Hope this helps.