Encountered FOUR golden rules of plumbing, yesterday.
1. You WILL need something else from the hardware store AFTER you get home and begin the job, no matter how well you plan.
2. The plan will change, most likely causing the above, but at least inducing 5 minutes of head-scratching while you inventory your parts
3. Once completely finished (HA HA), something will leak. Bad enough to put you back to work.
4. Something will happen that makes no sense at all. (in this case a leaky fitting stopped leaking when I attempted to take it apart)