Easiest and cheapest thing I have found is going to the dollar store and get what is called "The Worx" toilet bowl cleaner. Put it in a pump jug and spray it on the toons. You will see the junk running right off the toons. Pressure wash and all set. A lot cheaper then toon brite
I just pulled my boat a week ago to take on vacation. Wanted to clean the pontoons. Went to the dollar store and picked up 6 bottles of Works toilet bowl cleaner. $1.89 a bottle. Put it in a pump jug and sprayed to toons. Took the river grime right off. Then just rinsed off with water.