I have a Ridgid 4 gal. vac. (WD4070) that I use with a Thein seperator for dust collection, mostly with a ROS. Does anyone know if a HEPA filter is available for this vac? I've searched the web but can't find anything. Could I get additional filtering by installing a bag in the vac along with the canister filter? I do have an air cleaner plus a DC, but would like to get the dust at the sorce. Thanks.