I found this discussion... it's a few years old, but has info regarding the Saniway vacuum history. Didn't see anything relating to which vacuum bags to use, though.
Since Sani-Way bags are no longer available (and haven't been for over 30 years), you might want to use Royal Canister (not tank type) bags. The Royal round canister and the SaniWay are really the same machine. The bags for the Royal work very well in the Sani-Way since they are the same size.
It really sounds weird but it works.....Take a 4 qt Model 40 Presto pressure cooker gasket, glue it to the underside of the lid, then you can use a big open mouth bag such as a GE canister bag.The PC gasket will seal the open bag, works great.