I've cleaned my 4 carts twice in a week and although after cleaning (just spraying off with water) they look fairly new they are not passing water very well. They seem to filter good for a few hours and then the pressure goes way too high. I will try the above cleaning methods. I was thinking of using Dawn dish soap to soak over night then maybe doing a Muriatic Acid soak. I've done this in the past with little success. It seems the Dish soap wash really didn't do anything without any way to agitate the water/soap solution. I put all four carts in a plastic 55 gal garbage can for soaking. And as mentioned above, if you can't get the oils etc. out then the muriatic acid wash is useless. Any suggestions?