The way I did it-back when I cupped my males....
I used quart and pint size canning jars to keep them in. I changed the water every other day.
I set up an assembly line of sorts using 5gal buckets.
One bucket had the like temp tannin stained replacement water
One bucket was the waste bucket
One was the cleaning bucket (
just clean/dechlorinated water)
I used an extra large soft meshed net that rested on the waste bucket and poured the Betta in it- then dropped the Betta in the waiting like temp clean jar of tanned water-Rinse and repeat....
On the first Betta-I had an already clean jar waiting to put him in-I rinsed his jar to use for the next Betta in line.
I have never had any health issue related to cross-contamination since all mine are healthy to start with and I generally never had any outside/unrelated fish in the fish room or if I did they would be in QT-so I didn't worry about contamination-if that makes sense....lol....
Since I cull hard-I rarely had more than 80-100 jars at one time and the more experience I gained the harder/heavier I culled to get these numbers down further.
IMO-quality is more important than quantity.....but that is just my personal opinion....
I kept the jars in my china cabinet with glass doors and this would help to maintain water temp that ranged from 75F-85F depending on the time of year. I kept cards between the jars so they couldn't see each other and water level about 1inch from the top to prevent jumping out-along with a quarter to half dollar size water lettuce (
that was swapped out weekly). I moved them from pint to quart based on their growth/size.