Since my repitch contamination issue, I bought one of the cheap electric pressure cookers. All of my mason jars for yeast go into with about 1/4 cup of water with the lid set loosely for a 90 minute turn at 15 psi. With the little bit of water, I feel confident the internal surfaces are thoroughly sanitary. Crossing my fingers, but it seems to have eliminated my issues with harvesting yeast and repitching. I should add I do not reuse Mason lids.
Slurry goes into the sterile water, and I give a good shake and cold crash. I then decant the clear-ish water and put in a bit of the beer from the harvest on top. This seems to work and remains good for a couple of weeks. Otherwise I build a new starter.
No contamination yet... but I have only been doing this for a couple of months.