bessa:
Dilution B is historically the most frequently used dilution for HC110. It is an excellent place to start, and many users of HC110 are more than happy to stay with it.
I happen to have a bottle of Ilford Rapid fixer handy, and there is an instruction sheet on the side.
You are right - 1 + 4 means mix one part concentrate with 4 parts water, to make your working solution. You can reuse the working solution, but you should keep it in its own container.
The instructions give information about capacity and storage life.
They indicate that the capacity of the Ilford rapid fixer is 24 36 exposure rolls of 35mm film per litre of Ilford Rapid fixer. You may ask whether that means a liter of concentrate, or a litre of working solution. A quick check of the fact sheet on the Ilford website clarifies that - it is 24 rolls per litre of working solution. If you mix up 600 ml of working solution, you would expect it to fix about 60% (0.60 x 24 = 14 rolls) of that.
FYI - one 36 exposure roll of 35mm is approximately the same as one roll of 120 which is approximately the same as one 8"x10" sheet of film.
Here is the link to the appropriate fact sheet:
http://www.ilfordphoto.com/Webfiles/2006130218312091.pdf
Besides considering the capacity recommendations, you should also be aware of the keeping behavior of the chemistry. There is information about that as well both on the instruction sheet, and the fact sheet.
The fact sheet describes two types of tests you can perform on fixer. The clearing time test is simple and checks to see if your working solution has lost too much activity while being stored. There is also a test for silver concentration, but that is more related to paper, than film.
It is probably best to make up the working solution in an amount that is just a little more than the volume required in your tank. Than use the tests recommended in the fact sheet for testing clearing time to check the fixer regularly. When the clearing time gets too long, or the capacity recommended on the instruction/fact sheet is reached (whichever happens
first) it is time to discard the working solution.
By the way, if you should start to do printing as well, it is best not to use fixer that has already been used for film as fixer for your paper.
Again, have fun!
Matt
P.S. When I made my earlier post about mixing HC110, it reminded me of an old memory. When my father helped me set up my first darkroom, amongst a number of other things he bought/found for me were a number of heavy, glass 64 oz (two US quart) bottles, with excellent lids. I used those bottles for years.