There are safety issues with the use of pump up garden sprayers. I had told an employee to clean out a sprayer that had been used to spray bleach/water.I made the wrong assumption that she knew how to clean it out. We filled it with water and acid to clean some ceramic tile and grout. As soon as we started our eyes begin to burn and the solution had a strong smell of bleach. I realized that she had not put water in the sprayer and pumped it up to spray out the bleach that was in the line to the spray tip. We left the area for a couple of minutes and then went back and sucked it up. No more problem after that.
It is a good idea to never make an assumption that someone else knows what may be common since to you. Just like you would not clean a gun until you made sure it was not loaded. Another thing with pump up garden sprayers is that some are for chemicals, some designed for acid, and some have pressure release. Over time the hose to sprayers may become soft or brittle. They may bust when adding pressure creating a dangerous situation. The spray handles themselves may also become damaged from the solutions and may stick open or leak. So ever so often inspect them and replace with parts needed to keep the tool as safe as possible. Rinse out tanks several times and spray clean solution through lines. Some chemicals when mixed can become very hazardous.