RE: Best way to completely dissolve PETG from nozzles?
Ultrasonic cleaning at 40khz knocked off most of the residual:
There still exists some PETG inside the nozzle (I lack the equipment to photograph there), but the outside is clean enough. I think the lesson here for the future might be to use a cleaning filament to clean the inside of the nozzle *before* demounting it, so that the effectiveness of said cleaning could be evaluated by direct inspection after de-mounting.
As it stands, though, it could be re-mounted, and then cleaned after-the-fact with a cleaning filament as described by bobstro above:
I find it a lot easier to push some cleaning filament at 265C to melt any leftover PETG, let it cool then do a cold pull or three. Takes a few minutes of effort plus cool-down time, but it works well.
Then, as long as it prints well, one could infer that the cleaning worked.
By the way, this is a genuine E3D nozzle.