1) Use fabric dye designed for canvas or cotton canvas duck only. Use two shades lighter than you think it will take when choosing dye.
2) Take the wet bag from the washer and expand from inside with your hands.
3) Add dye to appropriate amount of water in a bucket or steel sink.
4) Submerge the bag and stir around allowing all the fabric to soak up entirely.
5) Remove bag from dye after a couple of minutes and sponge off any remaining wetness with a rag or old towel.
6) Let dry in the sun for an hour.
7) Go to step #5 in the distressing process."

I personally only wet the bag in a sink first. After it was thoroughly soaked, I added salt per the instructions on the dye packaging, and dye to a metal sink. I let it soak completely and did stir it around a bit. I let it stay in for about 10 minutes? Perhaps longer. Wade suggested a couple, but after a couple, I did think it had not sufficiently darkened.

Anyway after that, I just let it dry in the sun, however, I also filled it with dry newspaper occasionally and replaced it whenever the newspaper became saturated with water. I think that helped speed it along. Worked out very nicely in my opinion. I think the bag is now the perfect mix of khaki/sand/olive green.