I just got my 500 installed a few days ago and cannot convey just how good it is. We were into the install when I ran across this forum (thank god) and someone was discussing 1/2 inch pex being undersized. If you are running pex, be sure to run 3/4. It doesn't say it anywhere in the manuals, but Toto will confirm that they are getting calls that the 1/2 inch pex might not work out so well but 1/2 copper probably will. We had to re-run the pex, but the wall was still open and nothing else was hooked up. 1 post on this forum was the only confirmation that I could find anywhere on the net. thanks!