I have read about the mud base as in Miracle Mud but not about using cat litter. I used old sand from an established tank when I started my 54. I didn't rinse it, just scooped it out of his tank into Totes and then dumped in into mine an hour or so later. I would not do this if I was going to immediately add livestock but if you are cycling the tank anyhow I would not be super concerned about a through rinse unless you have a lot of
detritus.
