Even with just hot water it's difficult to shift if it's been on for ages and is well and truly baked on from the sun. I pump some Traffic Film Remover up an old WFPole, leave for 5-10mins then scrubb and rinse off with hot/cold water, repeat if necessary. OR with a 'Tucker' detergent dispenser add some cleaning tablets and WFP, leave to soak 5-10 mins again and WFP off with a scrubb and hot/cold water, repeat if necessary. Either method works but the hotter the water the better!