The YT-800 is an electricity-operated remote controlled submersible robot for cleaning large underwater surfaces, such as the bottom of a sand filter. The powerful pump and wide nozzle make it possible to clean large areas in a relatively short time. The sediment is pumped through a hose to a designated point of discharge, such as a sand treatment station. Traditional cleaning using loading machines, conveyor belts and such require costly investments and manual filter cleaning is very labor intensive. Both methods require that the filter is drained and taken offline. With the YT-800, cleaning can be carried out during full operation.