Appropriate rooftop water tank cleaning and disinfection

I'm working on an urban project in Tripoli, where water quality is a major concern. Almost all residents are living in 3-8 storey buildings with piped water that is stored in rooftop water tanks. These tanks are never/rarely cleaned, so residents are complaining of sand, algae, etc. It's unclear if water contamination is due to the tanks or the pipes (it may be both). 

We're setting up WASH Committees in buildings to maintain shared facilities, and want to come up with a relatively short tank-cleaning procedure that we can train them to perform. The cleaning and disinfection procedures that I've found so far entail lengthy soaking time (anywhere from 6-24 hours), which may deter them from cleaning the tanks regularly. Has anyone found a shorter procedure that is effective and easy/safe enough to teach residents to do themselves?