The rock has a PVC coupler inside that the face of the pump friction fits into. It should be near the surface so it can be accessed easily when the pump needs to be cleaned. It is OK if it is half way up in the tank, just don't pile a bunch of rock on it, grow hardy stuff on it like polyps and mushrooms that won't suffer too much from being abused a little. The rock is ceramic and will look a stark whit when it arrives but it does grow coralline quite well.