The HP Combi-Plan T is an ostensibly invertable daylight processing tank for 4x5 sheet film and glass plates. Unfortunately, it seems to be one of the only options for 4x5 daylight processing. I can't seem to find any of the long-discontinued Paterson Orbital processors that Katie Cooke raves about for sale in the US. Other than that, as far as I know, the only other option is a rotary tube processor, which is expensive and bulky.
Once you get the film carrier assembled (the instructions are sketchy) the film carrier is actually nice. It holds six sheets of film or glass platesdetermined by how you assemble the itand is easy to load thanks to a well thought-out slotted guide that fits over the loading grooves. Feed a sheet into each of the the slots and you're good to go. I think it would be great for dip and dunk processing in a darkroom as the whole unit picks up easily without disturbing the film and seems to drain well. But if you have a darkroom, you probably wouldn't buy a daylight tank, would you?
The problems start once you put the lid on. It's difficult to tell when you've got the lid all the way on by touch, which does not fill me with confidence. I'd rather have knowledge certain that the lid is on and light-tight before I take the tank out of the bag ino the light.
There are two fill/drain spouts sealed with caps, one on the bottom of one of the sides for drainage and one on the lid that a small funnel fits into for filling. (If you have a hose to your faucet, you reverse the flow for washing by hooking the water up to the bottom plug and it overflows out the top.) To fill the tank, you cap the bottom spout, affix the funnel and open the top air vent (accomplished by twisting the spout), and pour your chemistry in. This is great in theory, but in practice, the funnel channel and air vents are so small that it takes about 40 seconds to fill the tank. Unless you're using a split-bath developer like Diafine that isn't terribly time-sensitive or are doing stand development with a high dilution, I don't see how you could possibly get even development with this thing as by the time the top of the sheet is covered, the bottom has already been covered with developer for quite some time. This is compounded by draining out the bottom, which takes about 30 seconds, meaning that the portions of film on the bottom of the tank get 1 minute and 10 seconds more time in the developer than the portions at the top. I think there's a word for that, and I think that word is "bad".
Why not just turn it upside-down and drain it out the top? Because this thing is a messy, leaky bastard. The lid seal leaks, chemistry leaks out the top air vent when you fill the tank, and chemistry blobs out when you remove the cap for drainage. Unless you turn it upside-down to get the chemistry away from the spout, but then the lid leaks, which it does when you invert the tank to agitate.
Speaking of the caps, they're held on by those little plastic fishing line fasteners that hold tags to clothing, the ones with a T on each end. The super-cheesy, ~0.25mm diameter kind that are almost sure to break. HP went to the trouble of making the vents that surround the spouts open and close by twisting, why not go the extra centimeter and have it lock shut completely and forget about the caps altogether? The system would still suck, but it suck less in that there would be two less pieces to lose and it wouldn't be quite as messy.
As is likely apparent, I have nothing but contempt for this thing as a daylight tankwhich is what it's sold asas it's a dodgy, leaky piece of shit. If you want a daylight tank, I recommend that you save your film, your money, your chemistry, and your sanity and skip it. If you want a film hanger for dip and dunk, this may be your ticket, as it loads easily and drains well.