The Clean Tank techs use a proprietary method of sweeping and vacuuming the bottom of the tank of debris and sludge while keeping the emergency generator system online. It is not necessary to empty the tank of fuel in order to perform this tank cleaning service.
The Clean Tank has leaned through experience that timing is key to the tank cleaning process. When a biocide is used, a one step process of adding that biocide to the fuel and cleaning the tank does not always achieve the results we and our clients expect.
The situation is similar to using a pesticide to kill cockroaches in a kitchen. Once the insects are killed, their carcasses and waste products have to be removed. Your tank has microbiological growth clinging to the tank interior as a slimy sludge-like substance. Once the biocide kills the growth, the sludge slides to the bottom and can be cleaned. There is a waiting period between the time the biocide is added and the time the tank bottom can be cleaned.