The heaters' supplied metering pumps will only push fuel, not pull it, and not too far. If the bus's tank is a long way from the heaters (as my bus's is from the rear bedroom's heater), you may need to install transfer pumps to move fuel from the bus's tank to the heaters' 10-liter day tanks. I use a pair of cheapo gear pumps that are intended for scavenging oil in dry-sump race engines, and they suck fuel from the bus's tank and move it to each day tank through 3/8" fuel hose. Each pump can completely fill its day tank in less than a minute, and I have a momentary-on toggle switch by the day tank that actuates a relay that powers the transfer pump. It works very well and is easy to use. I had a spare 1/2" port in the top of the bus's tank, so I drilled out a 1/2" brass reducer bushing's thread and soldered a 3/8" stainless pickup tube into the bushing (yes, you can solder stainless!), with the bottom of the tube a few inches above the bottom of the tank. So far, so good!John
as noted, add a pump to fill the day tanks for the heaters.A really slick, idiot proof solution involves the vent being a return line to the tank.Run the pump until there's trickle, and it's full.happy coaching!buswarrior