Emptying the tank isn't a problem - just turn on the taps.

As a rule, I like to empty, rinse and refill the water container every day so as to ensure a supply of fresh water. We have the removable container under the sink and a full one just about does a day's water usage anyway. It's also useful to pitch up not too far from a tap!

With Covid-19 many of the shower blocks/toilets are not open so we bought a shower tent and a colapz shower and tank, to shower in. Having a full wash in the Troll bathroom requires some Houdini tricks and twists, having a shower in it would be very unsatisfying (apart from the shadow theatre effect on the window).

I would like a whale pump to full the internal tanks from an external tank when needed. One trip to the tap, internal water tank for those short weekends away. Has anybody got something similar?