Basically, one puts the rocks, the grit and a good bit of water into the tumbler. The grit and water create a thin sludge. The opening of the tumbler isn't very large, so sticking a hand in to fish things out won't work. I can get a finger about halfway to the bottom of the tumbler (which makes cleaning it not fun).

The only way I've found to get all of the rocks out is by dumping the contents of the tumbler into a sieve and then filling the tumbler with water several times, dumping it into the sieve each time. The grit sticks to everything-- the tumbler, the rocks, the bowl I use to catch the water (heeding the dire warnings that the grit will solidify and block pipes if dumped into plumbing), my fingers-- and has to be rinsed off the rocks before they can be inspected.