So, piston pumps aren't good with wettable powders. What are they good for? And what's up with the Echo that has a piston/diaphram pump? I've used wettable powders in a B&G stainless pump sprayer for years. They needed parts replaced occasionally like O-rings and plunger cups. Is that about like the backpacks? We need a FAQ page for stuff like this, I think.