Using 3 cotton cloths only. Each item was in the tube long enough for 3 changes.. I think this took about 6 hours total. Every change diminished the highest element in all my experiments, but after 11 events I got a purity increase of 4%!
First slot:
Original: 3.42/78.55/15.15/2.90/52%
1st change: Clearly Unstable 4.79/76.85/14.55/3.82/48%
2nd change: Clearly Unstable 7.01/75.26/14.34/3.39/45%
3rd change: Very Unstable 7.38/77.09/13.33/2.21/49% (this event gave purity increase)
1/11 or 9.09% chance to increase purity and main element in my small test