I found this 4x5 processing tank in John's Camera Corner, a used camera place in Blacksburg VA... 'tis a dangerous place to visit, things keep following me home. I have no idea where it came from, but I found a picture of it in the manual of an Omega D-II enlarger (roman numerals), where it was referred to as "PH 256a". The top reads "Adjustable cut-film-pack developing tank, patent pend. Fink-Roselieve Co., Inc New York".
It will hold about 1.5 liters of chemistry and up to 12 sheets of 4x5. The panels with the curved guides for the film slide into slots in the tank, to allow the width to be adjusted to process 3x4 etc. The lid does not seal and there is not a lot of room above the film, I typically get chemistry everywhere when I use it.
To load it, I cut a set of 12 of 4 inch wide 8 1/2 inch long strips of paper. I load the paper strips into the 12 slots in the light.
Then in the dark, I push the whole pile of paper to one side, slide the negative down along the left-most piece of paper (base side to the paper), and then pull the paper out and repeat with the next one. I can feel the side edge of the paper, and use that to position the edge of the film.
I typically hold the paper with my right hand, and the film with my left. (However I needed to hold the camera...)
After I have all the film in, I then go down both sides, and count the edges of the film with my fingertips. If I can feel 12 edges on both sides, then all the sheets of film are in their own slots, instead of doubled or off by one and diagonal. (diagonal ones feel like a single piece of film.)
The lid consists of a piece to hold the film down (shaped like a square bracket with a handle, it can be seen in the second picture on the left), an inner lid, and an outer lid. I put some rubber bands diagonally across the lid, looped under the corners, to make it slightly harder to knock off.
My agitation procedure is to put the tank in a tray with a piece of teflon sheet in it, and then slide the tank back and forth on the teflon. I spill about 150ml of developer in the 10 minute processing time. I have gotten noticeably uneven development only once. I agitate for 10 to 15 seconds every 30 seconds, and rotate the tank 180 degrees each cycle.