Over time the build up of silt is likely to reduce the capacity of sewers causing bottlenecks and blockages. Flushing improves the flow of water, reducing the possibility of pollution. HPWJ 'washes' through suspended sediment; the outcome of which is dependent on flush volume, the rate of discharge, th length, slope and flow rate of the sewer and it's diameter. Ultra high pressure jetting is capable of removing tree roots and scale. High pressure jetting removes general debris like grease and silt.