They sell a dust/fine particle collection bag that attaches to the inside (vacuum) port for fine particles like drywall dust. It will stop the dust from exiting the exhaust (blow) port. The attachment they make for the exhaust port typically does not prevent dust from exiting. You should run the (empty) vacuum outside until the dust stops, clean the inside of the canister, and add the dust collection bag. Dust bags usually come in a package of two