I'm assuming you mean the Patterson System 4 tanks. I've just checked my 2 reel tanks. 35mm needs 290 ml, so we'll call it 300. 120 needs 500 ml. The higher capacity tanks are the same diameter only taller, and the fluid requirements per roll should be more or less the same. Figure 2.5L for 5 120 rolls or 2.4L for 8 35mm rolls. There's no way you're going to get away with using twist agitation with that much film and fluid in the tank, so you'll need to invert it. Count on at least a bit of leakage, so use a bit more fluid than the minimum requirement so the top reel isn't left high and dry. I know that these tanks are quick to fill, but even so, that's a lot of fluid and could take some time to fill.. You might want to consider filling the tank and dropping the spindle with the reels into an already full tank.