I am growing out eight in a 55. A 75 would be much better. They were three inch fish when I bought them two and a half months ago. I am using a couple spare 55s to age water. The tanks are all drilled about six inches from the bottom on the back side and plumbed to a drain. I siphon the bottom, starting the siphon with a drill powered pump, then open the drain valve, and refill with a submerged pump in the aging tank. Lastly refill the aging tank by opening a plumbed in valve. All said it takes about 25 minutes. We do this twice a day. Once a day would be enough, but twice is better. About as much time and effort as some walking a dog. Oh, we feed four times a day. Beef heart before the water change, pellets once, and FDBW once.
There is more than one way to skin a cat. You just need to find what works best for you.
The 25 minutes was an estimate. I just did a WC. It took 9 minutes to siphon, drain, and refill. It took a total of 17 minutes including topping off the water ageing tanks. I usually top them off after every WC, but I can do it every other WC. It really does not take very long if you set everything up from the beginning to make it easy.