I didn't have any food coloring, but did this instead. I shut the supply valve off before going to work and when I got home the tank was almost empty. The water was in line with the flapper, so I assume its the flapper the way its sitting. Tried 3 different flappers and still the same. Noticed the fill valve was intermittently dribbling water on the top opposite to the dial where you adjust your floater height. Tried a different fill valve and the same thing. I have tried many combinations of flappers and fill valves and still the same issue of it filling itself up for a split second every 5-10 minutes. At least I got the slow filling and water hammer fixed.