@Laird_Popkin have tried keying the surface of the part before applying the dip coating? you could go as far as designed-in surface texture to allow for better bonding.
It takes me about a foot of filament to clean out the old filament even after heating the hot end to temperature and backing out the old filament.
A dedicated printer would be overkill, but a dedicated hot end would perhaps be an idea.
@ThantiK well you better stop breathing as there’s more chance of contaminated particals entering you system this way. And second stainless steel and aluminium both require certification to prove they are food safe. But only in certain counties so is yours one of those countries
@Nigel_Dickinson brings up a good point. The fumes can be bad. You may want to keep kids out of the room you print in. One guy was killing his fish with ABS fumes. They can give adults headaches. I don’t think they would be a good thing to expose a little kid to.