@Glen Bundesen I have an inline Normally
Open 12v Micro Solenoid on the mains pressure JG line directly behind the vans mains pressure filler inlet. My valve remains open and does nothing until it is powered. These valves are high pressure, non restrictive flow, 0.6amp, cycling in under 1 sec .... and most importantly are cheap at around $20.
My solenoid is wired directly to the water pump. My need was to have easy and switchless access the vans tank water whilst connected to a mains without needing to go outside and turn the mains tap off, and importantly without having a required constant power to operate. When the Drifter pump switch is activated the solenoid shuts off the mains and the pump is able to drawer only from the tanks, when the Drifter pump switch is turned off the solenoid opens the mains and returns the van to mains pressure. Has been working very well for 4 years now, and in the event it fails ..... nothing happens and everything still works
An inconsequential byproduct is the toilet also shuts of the mains whilst its flushing and also the solenoid briefly shuts whenever we use the pump when off the grid freecamping. These brief activations are negligible and doest affect my battery life so I can live with it
As you suggest, adding a Normally
Closed 12v Micro Solenoid to each tank line with the solenoid wired through a A/B switch to the water pump will work fine. Mine does
Im not sure Id bother with the bypass, seem very convoluted for a
what if. A simpler alternative would be use Normally
Open 12v Micro Solenoid and label the switch in reverse, so selecting the switch labelled "Front Tank" actually just closes off the Rear Tank. That way a system failure would just leave both tanks open. I think I would prefer that anyway.
Jayco tanks will decant between themselves ie all water in the rear tank going uphill and all water in the front tank going down hill. Inline check valves would stop that in the Normally
Open 12v Micro Solenoid setup