I do not keep brake fluid anywhere in the system- I drain the calipers, lines and M/C. Just to go that extra step further, I also take the calipers apart to clean them- there are only two bolts and it is a lot easier to clean the caliper halves w/out having to work down in a well.
By the time my brakes need changing, the system could use new fluid anyway and it also gives me a chance to inspect the piston seals for any weepage before they leak like a sieve.
But that is just me and I realize that most people just push the pistons in and replace the brake pads.
Brian
How do you keep the brake fluid in the lines?