I have a 25 gallon spray system built for a walker. Uses a disphragm pump attached to top of tank. The main problem I have is that I can't get all of the liquid out when I spray because the pickup line is inside the tank rather than picking up from under th bottom of the tank. Not a problem when you keep spraying the same chemical one tank after another, but sometimes I want to spray 5-10 gal of a specialty chemical for har to control weeds like nutsedge. I usually have 1.5-2.5 gallons left. Anyone seen a tank that has a sump formed in it to help get the last amount of liquid out. I was very hesitant to put a hose connection to the tank drain, because a break in the hose would allow all of the mix to fun out with no way to stop it.