I used to use a shallow can like Skippy's Peanut Butter and put just enough oil in it to completely submerge the lifters. This was left overnight and then placed on the drill press with a dummy push rod in the chuck. With good lifters many would self bleed overnight and on the remaining one a few strokes of the push rod would make them rock hard--no movement at all. On new engines designed for hydraulic lifters only you void the warranty if you pre-bleed the lifters. They want the new lifters to mate to the new cam while still a bit soft. This is probably from doing away with the zinc and phosphorous in the new oils.
