Be careful that you don't over-tighten the drain plug. Screw it in hand tight and only with a wrench a bit more. Check for leaks, tighten a bit more if needed. If you have a metal plug be very careful when threading in and tightening it, if you mess up the threads on the tank it could make for a very expensive repair, like a new tank. That is why the plugs are made out of nylon.

Those drain valves certainly fit in tight spaces, but I find the handles hard to turn. I prefer to use a brass valve with a handle. Here is a photo of the installation on my Hi-Lo:
https://www.hilotrailerforum.com/f27/...allation-2903/