Although my trailers have always had the anti-freeze fill, I understand it may be optional on some trailers; probably those sold in the deep south. Jayco does offer a optional kit to add this on (have seen it referenced here on JOF), or you can build your own from simple parts (2 valves and a T fitting plus a length of vinyl tube). The quickest solution is to get a bit (2-3') of vinyl hose the same size as the unpressurized feed from your FW tank. Pull the FW hose off the suction side of the pump, push the new length of hose on and pop the other end into your anti-freeze bottle. Just remember to put the FW feed hose back securely in place when done.
2011 Jayco X19H (purchased 2015)
2008 Jayco 1007 PUP (purchased new, traded for the X19)
2012 Chev Traverse LT with TP