It is important to keep in mind that pressure and the amount of water are always relate to each other. An high pressure can damage the drainage pipes and the natural water permeability of the pores in the soil around them.
Homburg advises a pressure of 35 bar on the pump, depending on the length of the hose this will result in a pressure around 10 to 15 bars at the rinsing head. The volume of the water will then be around 70 to 90 litres a minute. This is sufficient to achieve the right cleaning for your drainage system.