[Titan151]

You could consider changing out the tubing. I am not 100% on this but I think I have heard that WW can leave a slight residue behind. I use it along with anti-freeze and have not had any problems. Unless you have nice Tygon stufff this is a pretty easy thing to do with a trip to a hardware store.

If it is bacteria, there is a good chance that allowing everything to dry out will kill it. This may be somewhat of a pain as the Heater Core can take time.