Don't gorilla grip the gun. It looks like it's designed for the whole hand to squeeze, but if you do that you're squeezing at fulcrum. It's like trying to turn a ratchet from the head and not the handle.
Squeeze the lever from the end. Seriously. Try it and tell me it's not easier. Don't try it if you're running hot water without heavy leather gloves though. The coupling gets blazing hot.
Also, cable clips if you're washing non stop. They don't last long so buy a handful, but if you drop the gun get ready to do a silly dance to step on it.