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.