The Hippo Auto Top-Up Valve. With the Hippo Auto Top-Up Valve There really is no need to continue manually topping up your water reservoir when this handy device can effectively do the job for you, only using gravity and the float valve, flexible pipe and the choice of two end connector fittings to fit most water tanks. Simply set up your water tank and hippo Auto Top-Up Valve in position in the system and it will keep your nutrients at a constant level. The Hippo Auto Top-Up Valve can be used where a ball cock would be traditionally used but has the benefit of the flat valve being concealed. This makes it much less likely to suffer interference from root growth (in hydroponic systems) or animals (in animal drinking setups).