It's not that the smaller machines 'draw' better - it's that under atmospheric pressure, only so much liquid is going to get shoved through a downstreamer.Jim, I dont know the physics behind "why" but for some reason the higher GPM machines draw less then the 4-5 GPM rigs. At least that is what I have read on the BB's
So when you start seeing that 80-84 ozs per minute is about the max flow one of these suckers can move. Then you can understand that a larger machine will introduce more water and therefore dilute the chemical more. You can increase the pressure differential that the downstreamer sees by using a delavan to supply the chemical - then you will see even better flow figures.
Personally even when you are sucking 80 ozs. per minute. A five gallon bucket only lasts 8 minutes of actual downstreaming time. In other words if you have a 5gpm machine sucking at 7:1. You will only have 8 minutes worth of actual soaping time before your 5'er is empty - and personally that's way too fast for me.