Originally Posted by cfsoistman
When you disconnect the hose water will run back out of the connection. These hose connections do not have a check valve so there is no trapped water in the line.
Actually the valve I am speaking of will be inside the rig not at the fill port. Whether you know it or not there IS a check/vacuum valve in that line. It is mandated by law so that fluid from the black tank cannot back flow and contaminate the hose and hose bib when they are connected to that port. When you disconnect the water hose from the line it relieves the pressure on that line, the valve breaks the vacuum and allows the water to flow back out the port thus stopping the possibility that a siphon can be formed to pull black water out of the tank.
In ground water sprinkler systems also have these valves as mandated by law and home bidet toilet seats also have to have them.
On the Georgetowns the valve should be installed in the line, inside the motorhome (ours is in the washer/dryer cabinet) and is much higher than the black tank(s). Someone here posted a picture of one inside their rig because they didn't know what it was. Depending on the supplier they will be different colors. Our original one was grey, the replacement that FR sent us was black and a different shape.