I've got a little experience with the pain and suffering spilled dye can bring. Putting RIT dye in a ziploc
bag sounds like the third worst idea I've ever heard. Perhaps if you have a big junk washbasin in your basement/garage this messy procedure would be okay, but for the rest of us who must do this in the kitchen, keep your liquid dye in an 8-quart spaghetti pot (only a couple inches of dye) and be careful, so friggin' careful.
You can pick up an 8-quart pot at any thrift store to destroy as you please, and it's roughly 5,729 times less likely to leak than a ziplock.
Plus, it sounds like the last step of the ziploc procedure is to dump the dye out of the bag down the drain. That's wasteful. Keep a pot of dye in the garage with the lid taped shut over some cellophane (for a good seal, and so the water doesn't evaporate away) so you can dye whenever. I used the same two boxes of black RIT for over a year- just keep adding more water as level goes down.