Why not buy liquid flux? I use 186.
I just Google “285 vs 44” and see the flux used in 285 is 186 in solid form. If you’re dead set on rosin core solder I’d choose the 285. The 44 is much more aggressive and will be MUCH harder to clean
Edit: read this
I stand by my first statement; just use Kester 186 liquid and standard lead solid core solder 63/37.