Did a roof the otherday similar to picture that G,L,R posted.
Just used pure water and it came up brilliant, customer well pleased.
Just gave it a quick soaking with the wfp and left it for a couple of minutes, then gave it a good scrub with pole.
If i have any problem marks on white pvc i use "PVC Cleaner" made by NILCO, otherwise just use the pole with pure water.
Craig
