Question: How can I clean a shop-vac filter without getting covered with dust?
Answer: A clean shop-vac filter will help improve suction and motor life. I always take my filters outside for their cleanings. With my canister filters I hose them down and use a toothbrush and hose to scrub the surface. If you use the filter while it is still wet it will clog very quickly. I keep two filters on hand to avoid this problem and alternate their use.
Another option (especially when it's too cold outside to use the hose) is to put the filter in a clear bag with a brush and tie off the end. You can then scrub the filter while containing the dust. When the dust in the bag settles you can remove the filter and dispose of the bag.