AWWA ACE61673

This paper describes a new rainwater tank cleaning system called "Tank Vac" which aids the regular removal of debris and sludge from the bottom of water storage tanks. The system relies on overflowing water from the bottom of the tank rather than the top using a unique siphon system. When the tank is full, a valve in the overflow line is triggered to allow water from the bottom of the tank to flow out the overflow pipe at a rate high enough to produce a full siphon. The magnitude of the flow creates a cleaning action at the base of the tank. After a short flush period, a ball cock allows air into the line to break the siphon and the cleaning action ceases until another high rainfall period. "Tank Vac" installations in household rainwater tanks have decreased E.coli levels at the bottom of the tank from 430 counts per 100ml to zero after a 4 month period and increased oxygen concentration levels markedly. A "Tank Vac" flush model is described for predicting the flush frequency over a calendar year for a given set of conditions; such as local rain fall, tank size, roof size, collection efficiency and household water use rate.