Yes, don't bother with the trigger, keep it simple.
Use a pole with an outside quality hose, and you just 'nip' the hose to stop your pump.
Also, use both a sack truck to transport the backpack, or carry it on your back depending on access. Or, depending on the area, use a sack truck to transport a water barrel, and carry the back pack on your back.
My round is mainly residential, with quite a few difficult to access areas. I reckon my backpack, used with a bit of 'common' is far quicker than what a 650 litre van mounted system would be; for my type of residetial round.
I/we also trad the ground floor, usually.