I though I can re-use developers as well. Maybe that's why I didn't found much information on reusing developers on Internet.
Most developers
can be re-used, but this is generally done at lower dilutions (often at stock dilution), and it works best for fairly high-volume operations, in conjunction with replenishment. This sort of use was once common for big photofinishers, and I suppose it's still common for commercial color photofinishers. There may still be a few B&W photofinishers who do enough volume to make it worthwhile, but they must be fairly rare.
Instead of re-using developers, most hobbyists use them at greater dilutions (say, 1+1, 1+2, or 1+3 for D-76 or XTOL). This reduces costs, much as re-using does, but it's less hassle and it produces more consistent results when you don't run dozens or hundreds of rolls a day.
You mentioned Ilfosol 3 in your first post. I'm not very familiar with that developer, so I don't know if Ilford even has data on re-using it. You mentioned that you've found capacity data for it. You might do some math to see how much volume that works out to. For instance, if it says "8 rolls per liter at x+y dilution," then you probably need at least 125ml to develop a roll, and you'll be fine with a tank that requires 400ml. If it says "2 rolls per liter at x+y dilution," then you might want to boost the volume you use to 500ml.
Looks like I can only reuse the fixer. I have on idea about what the film will look like if it is not clear("fixed" another word). According to your comment, seems that I should take a little piece of film and put it in the fixer to figure out the best fix time for that film, is that right?
Yes.
Which should be done after developing and stop bath, right?
No, you do this before you develop the film -- you cut off a small amount when you load the developing tank, set it aside, and before you begin processing you dunk it in fixer. You can do this in room light. Without developing the film, this will result in a completely cleared piece of film, assuming the fixer works at all. Double the clearing time is your fixing time. (Some people say three times the clearing time, either for all films or just for T-grain films.) I use double (or triple for T-grain films) the clearing time or the manufacturer's recommended time, whichever is greater. This is usually the manufacturer's recommended time, except for a few films when the fixer is nearing exhaustion.
FWIW, getting a spare scrap of film is easy with 35mm -- you just use the leader that you cut off to load most tanks, so there's no risk of cutting into your actual photos. With MF, you can also cut off a centimeter or so from the start or end of the roll. Depending on your camera, there's some risk of cutting into your image when you do this. Alternatively, you could sacrifice a roll to use for test snips like this, but it should be the same type of film you're processing, since clearing/fixing times vary between brands and types of film.
