If you wash the shampoo off your car/van off with a hosepipe it comes off lovely. If you missed a bit of mud when washing with shampoo, you put your finger over the end of the hosepipe to inrease pressure ad 'blast' off that bit of mud. I mistakenly bought fan jets and subsequently love them to bits...they blast through snail trails and green conservataory roofs simply by having more mehanical abrasion, that is provided the flow rate is high, really high so you an see a rainbow when the sun is shining.