diluting HC-110 is a 2 step process by the manufacturers
recommendations (1st dilute to stock solution, then dilute to
working solution when required) generally however there is a
Dilution 'G' (or something like that... someone will be able to
correct me) that is a direct one step dilution (1:63 I think??).
Since HC-110 is so thick, measuring the amount required for a
500ml tank (or 250ml if you're only doing one roll) can be
difficult (or you get it as close as you can and don't worry
that you've actually got 1:50 or maybe 1:75). For my Paterson
System 4, 2 reel tanks, I use about 550ml or working solution so
that any bubbles are above the film!  Also, for your stop bath
'rinse', just use tap water unless you've got a reason not to.