As far as draining, look under the RV below where the tank is and look for a single pipe. You may find a pipe with just a cap on the end, or a valve.
If you find the pipe and it is just open ended, you'll need to locate the tank inside the RV and there may be a drain valve there leading to the open pipe you hopefully found. NOTE: You may also find a open ended pipe which could be a vent.
If you find 2 pipes side by side, they're most likely your low point drains for draining the entire system.