Jamie,
It's called a Spray Master. I've tried them too, and they do work awhile; longer than any I've tired. They are a great company to work with as far as holding up the warranty...send a new one right out.
I'm trying that sprayer right now, but each time we get done using it, take the sprayer out and empty, and put a cap on the bottle....seems to be working...
I think letting the sprayer sit in the fly spray solution is ruining it....