No you need to drop the tank, the fuel lines are pressurised so you risk forcing fuel through the Webasto pump, you can do it on some vehicles return pipes but not on yours, tank drop is easy if you can get the van up high enough, I have a two post ramp so very easy but can be done on your back, make sure it is well supported on heavy duty stands on all 4 corners, as high as you can get it, have less than a 1/4 tank of fuel in too, it's definitely a two man job though.