I had a slight dip in the fill and vent tubes. They would fill up and act as a blockage, especially the fill tube. That allowed water to flow back out the fill tube and the tank wouldn't fill. My fill and vent tube is accessible under the sink. I used wire ties to pull the tubes up separately to support them so there is no longer any low spot.
I also made my own filler hose like mike-s uses. Mine is about 24 inches long and will go all the way into the tank. I can fill the tank as fast as the hose will allow. There is plenty of room around the filler hose to allow extra air to escape back through the tanks fill hose. When I hear the tank fill hose start to gurgle I slow the fill rate until the water starts to back flow so it won't bulge the tank. At that point the tank is full and I shut off the hose.
