Thanks Mike, all connections were tight... I checked the forums here first
But I learned something today after, of all things, reading the owners manual! I couldn't get suction at all in the winterized setting, so, as the manual said to try, I opened both low point drain valves and tried to prime the pump by holding my fill bucket as high as possible, sure enough I got antifreeze flowing out of the low point drains. Stopped the pump and shut the valves. The thing drew in the remaining gallon of fluid within seconds and pressurized the system so I was able to winterized without further issues. Took almost 2 gallons. I didn't have new mysterious clear tube to bypass the filter housing, so it had to fill first. After I got done I removed the filter housing and used the antifreeze in there for the bathroom traps. I think I'll just bypass that filter next year and go with an external filter only. Now my only worry is about the little bit of water still in the bottom of the water heater, and there must be water in that little bit of hose at the bottom of the water heater before the bypass valve. I think I'll disconnect that fitting on the bottom of the water heater inside and see how much water comes out.