One morning my wife Lois asked why our water tank did not overflow from off the base. As she pointed out, a base overflow system should keep the base of the tank clean and when the tank was filling the new freshwater would be retained while the older water was flushed out from the base. Could it be done? A quick trial using a plastic drum with some 20mm pipe proved that an overflow could draw water from the tank base. We needed to have a system engineered so that the Tank Vac could be installed into a full tank all from outside of the tank. At Waikato University Engineering staff under the direction of Dr Michael Walmsley carried out the necessary research require to establish the best design for the system. At Waikato University there is a very modern large scale laboratory in which the development and testing was carried out. What size should the pipes be? What direction should the vacuum holes point? What size should the holes be? How many holes? How to control the overflow so that the tank level did not fall below a particular level?