Don't leave these guys outside even if you think you've purged all the water. Last couple of brews have had that "homebrew twang" to them and I couldn't figure out why. Last night I noticed the kettle was about 4 gallons down, but my 15 gallon fermenter was overflowing. Looks like the brazing expanded during a freeze last winter and I was leaking hose water in with the beer. Last night I had a kink in the outflow of the water side and had too much back pressure, sending cool, fresh, chlorinated water into my fermeneter along with the wort. I thought something was fishy when the wort was chilling so quickly.
Luckily, I still had 7 gallons left in the kettle, so I was able to save some of the batch.
I always purge the water, but it doesn't take too much to push coper out to place. Time for me to start thinking about a counter flow.