bunker solution has worked best for us.
Simply hose bunker down with water to get surface wet.
Put bunker solution into pump sprayer and lightly mist the bunker
Let sit just long enough until it attempts to dry
Rinse with water
It's that easy, saves a lot of time and keeps bunkers looking fresh
if you have really old hits, might have to deflate bunker and let solution puddle ontop of the stain, but it will get it out