Have you ever tried a hose end sprayer. That's what I used to use on fruit trees. It'll spray a lot higher than a pump up sprayer.
Every time I get done with my pump up sprayers, I hang them upside down with the pump mechanism removed. I also lock the spray wand on and hang it so it will drain out the tip end. Never had one fail if I hung it like that. I do it every time I use them, because I'll forget to winterize them if I don't. It's the pits to be old and forgetful, but I was once young and forgetful too. I have three pump ups. One for garden bugs, one for brush killer, and one for cattle spray. One is an old Spray Doc brand, other two I can't remember.