Well catch me out, you'll get caught out by hepatitis, why not go for something with a virus killer on it too like the hydropure or aquapure, filters or kills all nasties, removes metals etc.
As for the back flush distilled water, why not use the water you have filtered?
Good point on viruses. I hike in Southern California mainly and usually go for springs and that's usually pretty safe to drink as is. But I totally agree with you, better safe then sorry. If i'm really concerned then I would drop some water purification tablets or boil it.
As for cleaning out the filter, you're right again about using the freshly filtered water!