I would get in touch with Grizzly Customer Service and ask them before washing a bag.

Wood Magazine has a ton of information on their website about dust collectors.

I wouldn't go further than shaking them out and vacuuming the inner surface. And outer too, because they get attract dust from the static.
Shake it off, shake it off. Say! that's catchy!
Casey

Washing them will certainly get them clean and increase airflow but at the cost of filtration efficiency. More fine dust will get into the air and your lungs won't thank you for it.

To get more airflow, the best method is to increase filter surface area. Replacing the bag with a HEPA cartridge filter made by Wynn will accomplish that. Using a cyclonic separator or a Thein baffle will help the filter stay clean longer.