I used some bambu sparkle filament and some sparkle made it into at least the first layer of my next print.
What is the best approach for flushing the nozzle after sparkle filament? Do I just do a small print with another color, or is there a button on the UI to do a flush with a new color?
There is no button other than to manually extrude. You can adjust the flush volume for that specific filament or as you said, print a sacrificial part.
You could try out one of the cleaning filaments but I am dubious as to their effectiveness. Nevertheless, it might work for sparkle filament.
I evaluated a cleaning filament simply because it was cheap enough and I wanted to find out for myself. I tried PETG, PLA and PC in various different colors during normal operations. After each filament change and before installing the next filament, I used the cleaning filament. In all candor, I did not notice anything deposited on the cleaning filament so I concluded that this stuff is more “feel-good” placebo than what it really is claimed to be. However, I did not test it on sparkle so YMMV.
I think just printing a small part will be good enough or printing a part that I don’t care if it had a little sparkle on the bottom.
I could only see it on the bottom of the part, and only a few sparkles.
There are worse filament than sparkle.
Try printing something with grey PLA-CF and then something white… 
I usually load the filament using the Load button and then extruder until everything looks clean, then I wipe the nozzle with a towel not to contaminate the next print.
Or if you’re lazy. then add a large skirt around the object.
I’ve been using the cleaning filament for a couple of years now, after every print I do with CF or glow or other additives. It does drag out a lot of impurities from the hotend. On the BBL, after an unload, I disconnect the PTFE from the extruder, manually adjust the temperature to ~250 and draw it in using the display controls until it comes out clean, then back it out again. It only uses about 15cm to do this. Next time I do it, I’ll try and take a close up picture.
I would look forward to seeing such pics.
This could help me understand if I am simply not looking for the right indicators when I used cleaning filament on my machine.
The wiki has instructions for a cold pull here.
https://wiki.bambulab.com/en/x1/troubleshooting/nozzle-clog
Not sure if it would help, just offering a link.
