Here's my question, if you water test first, then drain then water - aren't there still impurities in the tank, plumbing? I filled with tap, tested the plumbing and drained. Then I went through the adruous task of cleaning everything including the plumbing with diluted vinegar. Think about trying to snake a vinegar swab through the 90 degree turns! Ugh! So, did I go through a little overkill, or was my assumption of impurities correct?