Just leave that valve as it is if you have never used the FW tank. Just watch it when you pump the antifreeze in. If you see AF going to the FW tank then you have a check valve stuck at the FW pump. If you have water in the FW tank, you should turn your pump on/off a couple of times to push some water through your system letting the valve reseat.
Richard & Jill
2014 Flagstaff 832IKBS Classic Super Lite
2018 Silverado 1500 Crew Cab Z71 4WD All Star Edition
Camping since 1989, seasonal since 2000
Car Shredder Op/Tech, Scrap Metal Recycling - retired
I deserve hazard pay when camping with my relatives.