I have a Jayco Journey 17.55.8 where the cassette toilet doesn't have a separate flush tank, it gets the water directly from the tanks. When I have been staying in caravan parks and connected to mains water I have had near empty tanks. ( At the moment I carry other containers with drinking water). My question is, does the water for the flush come from the tanks or from the mains. Whenever we flush the water pump starts so I am confused as the where the water comes from.