Conflicting instructions on refill tube with Fluidmaster universal repair kit
I'm guessing that if the refill tube is placed fully down the overflow pipe it is possible to setup a siphon, pulling the water valve open and using large amounts of water.
The correct installation is to use the clip so the refill tube is aimed at and enters the overflow pipe. There should be a visible air gap between the bottom of the refill tube's nozzle and the top of the overflow pipe. See the attached image: