if you skimp on flow rate then its bound to have some affects - i like to have it about 2pm to make sure the windows get blast rinsed off at the end..
davo- it would work linking them all together but you would need some nice clear hose, so you can see whats happening, and hoselock do a brass y peice with a brass tap on eack side, so get however many of those you need and Y them all together through the barrel lids, then you would just have to close off the other taps, and have one open, though youd still have to go back to the vehc to do that. I have just got a 250ltr flat tank with metal straps which only just fits between the wheel arches of my estate so that will help, i hate changing barrels.