Just used the sprayer with a mix today, and I had this bright idea. On the bottom left side of the tank is located the drain plug. Now, before I mixed the chemical, I was considering what I would do If I did NOT use all of the solution. Having worked with sprays before, I knew better than to allow the mix to remain in the hoses, nozzles, pump. This stuff can gum up and cause all kinds of problems. I really messed up a steam vac before by being lazy and not cleaning the lines after use, took forever to clean it out.
So, to the drain port, I removed the cap and connected a three foot length of garden hose. Here I have a female connection on one side and a male on the other. To the male end I placed a cap, much like the one that goes to the tank. This hose I will leave on the tank. I just weave it through the rack when tank is in use. When I finished, I quickly removed the cap while inserting hose into a can of appropriate size to hold the excess. On the next use, I'll simply add back to the tank. Following this, I was able to rinse the tank without wasting my mix or causing a problem by dumping.