It must be the 500 - takes 1 1/2 inch hose. Been trouble free for 20+ years in the same service before needing a new diaphragm. Winterizing is nothing special. Pump out the tank, run in some RV anitfreeze through the head, and leave it in the tank. No attempt to run the AF through the guzzler. Maybe Bosworth is cutting costs on the newer pumps, cheaper valves, making things better for Bosworth (in the very short run). BTW, if your Guzzler is installed horizontal, it's important to install the little flapper valves so gravity tends to close them.