I dunno i just pop in the dose of dechlorinator for my tank size and fill er up with a garden hose, and do 75-90% water changes weekly
Id love to see anyone have enough space to have holding tanks of water enough for 100g+ lol With all my tanks combined I have roughly 200 gallons id have to have stored in holding containers, thats really not feasible for many people. And with bad joints in my hips and shoulder, I'm sure not carrying buckets around either.
I'm not bothered to get a python. I just use a regular siphon hose to drain the tanks into my bathtub, then another hose to refill.
And for the record, when I was new I forgot to dechlorinate a tank and didn't realize for at least 8 hours, once I realized it I dechlorinated the tank, but the fish was perfectly fine lol its not necessarily an instant poison.