The following may not be necessary, but can be reassuring nonetheless. Pre-rinse towels really soaked with darkroom liquids immediately in the darkroom to get 99% of the solutions out in your darkroom, thus sending that percent of the solutions down the drain, then keep the rags wet so the fix or whatever doesn't get a chance to really embed itself into the fabric. Then, wash on the heavy duty extra soiled fabric "grunge cycle" setting before the towels ever get the chance to dry.
Now for the parts I do...
1. Use worn out old bath and kitchen towels and the like for the really ugly cleanups in the darkroom like wiping up the sum of chems and shoe dirt on the floor. I use the ugly old towels so they do not become part of the ordinary household towel ecology.
2. I have special rags and towels for the day to day hand drying and less nasty cleaning in the darkroom. They too do their work only in the darkroom so they do not end up in the bathroom or kitchen. I found some hand towels for super cheap in a Bed and Bath store I think. Packs of three for a couple of bucks or so. I couldn't pass them up. And since no other towels or rags in the house match them, there is no confusion of what towel goes where.