Good Evening, Brian,
I presoak in the drum. I use a Chromega drum with four-sheet capacity (4 x 5). Although it was designed for color print processing, it has about a dozen small, raised ribs running lengthwise and spaced at intervals around the inside circumference. That seems to be enough to allow liquid to reach the base side of the film. I've never had any problem with the anti-halation coating; usually it pours out with the pre-soak. I can see the possibility of problems with drum that's completely smooth inside (e. g. Cibachrome). What brand of drum do you use?