I used to use the washer, which worked really well with polyester-felt socks, which are quite soft and pliable.
Later I switched to polypropylene socks, which last practically forever, but they are rather stiff with a singed surface. The washer didn't work as well with them, and I then started using sand substrate. I didn't want to mess up our new washer with sand, so I switched to a soak in a strong bleach (Clorox) solution followed by the turning them inside out and spraying them with a garden hose. The bleach dissolves out a lot of the organic matter, then the hose nozzle blasts out the residue and sand. Turning them inside-out is the hardest part, but they do get more pliable after you do it a few times. I have enough socks so that I can let them air-dry for a few weeks, so chlorine isn't an issue.
If you have a sand substrate then you may want to rethink using the washer, sand has a very abrasive effect on your washer's pumps, seals, and such.
