Connecting two Aquarolls

Desertjock

Could anyone give me some advice on how to connect two Aquarolls together so that they automatically switch from the empty to the full, or automatically fill the empty one. I'm new to caravanning and have always stayed on serviced pitches. We are staying
for the first time on a CL and would like this setup as I've seen on a few vans. Also, I intend to use the on board 30 Ltr tank as well. I presume it would be a case of switching the valve from internal to external or just filling up the internal tank again.

Some may call me lazy!! But it would be nice to avoid another trip in the mud. Thanks.