I have the Combi-Plan tank, and it works fine, even with the small opening and funnel. You mention that you're particularly interested in using it for semi-stand developing, which implies a highly dilute developer, and long developing times. Do you really want to stay in the dark that long? Another option that I've done with the combiplan tank is to fill it with developer, go into the dark, load rack, put it in the developer, start timer, do initial agitations, then put top on. Now the lights can come on, and you can finish processing in the light.
Originally Posted by JeffD
Another daylight tank that works well is the Nikor stainless steel sheet film tank, but you'll have to get one of them used, as they're not made anymore. It holds 12 sheets, and is adjustable from 2x3 to 4x5. I use my Nikor tank for 95% of the sheet film I develop.
If you're really set on using 3 tanks, I would suggest just buying 2 more of the Combi-Plan tanks, it can't hurt to have spares! And being that the rack is plastic, just like plastic reels, it has to be dry when you load it, so if you're going to develop more film after you can just use the 2nd and 3rd racks while the first one is drying.