Nice to know others are doing the same thing that I had in mind. I have general pump's version of the x-jet and it has way too much mist and uses too much chemical. I dont like downstreaming either, because i dont want to go back and forth to shut the chemical off all the time. Ive been rinsing with the same tip I apply chemical with. (pretty much a straight jet of water under low pressure. You could use a garden hose to do what I do). Then even if i go back and shut off the chemical, I still have 150-200 ft of water in the hoses that has chemical in it.
For this reason I am wanting to build a chemical sprayer dedicated to applying chemicals (i mainly wash houses) My thought is to take a 15 gallon chemical drum, mount it on a cart/hand truck (or dolly whatever you want to call it) and put on a pump/battery on top and some hose. Probably a little hanger somewhere on the dolly/cart to wrap the hose around on. Then use this setup for my chemical sprayer. I have a 15 gallon sprayer already that has a 1gpm pump and would take a 2' x 4' wagon to tow it around. Its not really ideal, only has a 15 ft hose and not really enough flow or pressure.
I have also considered using a hypro roller pump (i have a silver series 7gpm pump on the shelf and a two different motors I could use to drive it) that is possibly trailer mounted (which would need several hundred feet of hose) or put it on a dolly/cart as well. I suppose a 5 gallon bucket or two would work as well and i could just put a pump and battery or engine on a cart and move it around.
One thing ive been using the most is a rechargable 5 gallon electric backpack sprayer. Cheapie from harbor freight but works great. Kinda heavy to carry around and its only got a 1gpm pump also but that might be able to be changed, the pump has the standard flange found on alot of electric pumps. That could be my best option? I dont know.