There could be a number of things that can prevent the tank flush water from flowing. One of the more common problems is that the flush nozzle gets plugged up. In that case you remove it and clean it out. Some people, including me, drill the holes out a bit bigger. Sometimes the anti-back flow valve can cause problems. In my case, I found the hose kinked right behind the hose inlet fitting where the plastic line had to make a sharp 90 degree turn. I replaced the portion of the line with a 90 degree PVC elbow.
Richard and Laura Mae
2007 Monaco Camelot/2003 Jeep Rubicon or 2006 Jeep Commander
From the Land of Enchantment, New Mexico