Does anyone clean out their bog? I have had mine set up for 10+ years. I've recently noticed a lot of sludge coming up through the pebbles. I'm on a group on Facebook and they clean theirs out yearly. I mean take out all the pebbles and empty it than put new pebbles or clean the old pebbles and put them back in. I always thought you were not suppose to mess with it. What's the opinion on here? Clean it or leave it?