Jo:
We use a Sears Craftsman shop vac, 16 gal, & I really don't know the HP. We use the Greenlee pistons (mice)and the Greenlee nylon string. (comes out the middle of the spool) I have never tried the baggie trick, but I may on the next job. We just finished eight UG PVC pulls (180' to 340' 1-1/4 and 2" Sch 80) and had no problems with the vac or pistons)
John (HotLine1)