First, pyro negs usually looks a bit "pale", as the stain density doesn't show in the same way as "normal" density shows, so the proof lies in how the neg prints.
PMK lasts for quite long, so that should not be a problem. But do test with a cheap/scrap piece of film.
Now, for the question about dilution. If your tank holds 500ml, you could try e.g. 1:2:75 instead (of the ordinary 1:2:100). This will make your dev-times shorter by say 20% or so, but you have to test to find out what your personal dev-time is.
//Björn