So I have several steel tanks - some had liners in them, some had some rust. Initially I had put them on a treadmill with rollers to just keep them straight. This worked well but wore the belt and wore a groove in the board under the belt where the tanks sat. This eventually wore the belt out, shredding it's underside and made it unable to keep straight without constant adjustment - i.e. I couldn't leave it unattended. The dive store also had given me a tumbling device to use if I could. Due to the wear of the belt it also couldn't be left for long. So I took the belt and floor off the treadmill and put wheels directly on the drive roller. Here's some pics:
Click on any image below to view a larger (around 640x480 pixel) image.
A movie of the initial treadmill tumble.
This worked but since the other rollers were suspended in the air, there was too much flex in the system. I added some cross bracing and the tumbler works very well - very quiet without the shaking or flexing. I then braced and cut off the rest of the bed area of the treadmill making it more compact. The white circle on the right is a thin piece of teflon which allows the tank to press on the edge but lowers friction.
And some pics of the tank rinser - also used to hold the tanks - upright to fill with media - upside down to remove media.