I throttle the water back, it helps move things faster. If you get caught with a near-full sprayer you can suck just chemical, but it doesn't seem to come out any faster. I think the water helps the pump keep it's prime. With a venturi you HAVE to have water, sometimes that just isn't workable if the sprayer is almost full. This way is flexible.When sucking chem, do you shut the water right off ? Or just throttle it back ? I assume that would be quicker than using Venturi to induct it out of totes?