Thanks Doug. That's a good idea. .
I made a sifter using a window screen, and it seems to work well, but it's a bit on the small side. I think that I will make a larger one out of PVC pipe. The problem is that when I wash it through the screen, the water eventually comes out almost clear, which is what you want. But, when I put the hose in the bucket and stir up the gravel, the water gets muddy again. My thought is that either the silt really sticks to the individual grains tightly, which I think that it does, or that the gravel actually contains bits of some sort of clay or rock that easily breaks down into silt as I stir the bucket.
I think that the former is the issue, because, after screening the gravel the first time, I put it in the tank and filled the tank, and the water was extra cloudy. The silt settled and eventually covered everything. Stirring the water around it did nothing to clean it off the faux wall or roots. I had to manually wipe everything down to get rid of it. Even then, I couldn't get into the nooks and crannies, which, when I made the roots, wanted to look dark. The silt in there changed the look of the wall, but honestly, it doesn't look that bad. And truly, it probably makes it look more realistic.
I'll wash the rest of the gravel today. So far, for 3/4 of a bucket of gravel, I put in probably 8 hours of washing it already. Usually filling a bucket of store bought gravel with water and stirring it up a few times usually works, and takes about 20 minutes or less. This is something else.