To reuse bags (keep. in mind I'm lazy and this is with coco/perlite), I empty them, turn them inside out, beat them a few times against the ground to knock off any media/soil sticking to the bag, and let them dry and bake in the sun (generally for days). If there are visible salt deposits on the bag, I'll hose them down. The resulting bag is not fully 'clean' (compared to a washing machine) can have some 'dirt'' and fine roots embedded in the fabric, but it's essentially sterile, not shedding any soil/medium and any dead roots are an insignificant amount and future plant food.