I usually hose down my batting as well... just clean off the worst of the gunk and throw it back in again. My betting lasted about a year, but was starting to lose bits into the pond, so I just replaced it this weekend...
I put my batting down as the first layer in the bottom of my skippy filters, then lay the green scrubbies on top of this. I found some 1" thick batting, and cut it larger than the barrel size (about 23" diameter to fit the 22" barrel) because the original piece didn't fit well around the edges and I had a lot of water flowing around the batting rather than through it. This appeared to have worked TOO well, as it created a back-pressure in my pipes and popped one of them loose. I woke up yesterday morning to find the pond missing a lot of water! So I cut slits around the center filter pipe to allow the water to flow up through the center of the batting and force the water through the media, rather than allowing the water to flow up the sides of the barrel past all the media. This relieved the excess water pressure, so all seems to be working now, and the water flow in the barrel is nice and smooth when it reaches the surface, rather than bubbling up around the edges like before.
Its raining like crazy here today (finally), but when I get a chance, I'll have to look and see how this new setup is working for polishing the water...