Do I have to drain the caravan to travel?

This may seem a simple question but I am a newbie :)  I have figured out how to drain the van using the plugs but wonder if I have to do this at the end of my stay to travel home? Second question is how I drain the water in the flush cassette toilet compartment? I do not know whether this should be drained prior to travel either. The van has a storage tank which takes an aqua roll to fill & then I fill the aqua roll again to top up the tank. It seems to be working! A lot of this is trial & error!