In a couple of my fishrooms, I've used the Rubbermaid stock tanks as African cichlid breeder tanks, grow-out tanks, tanks for big fish (lungfish and bichirs) and for aging water for my auto water change system. I like the 150g size as it is big but has a reasonable footprint.
They're plumbed with a 1 1/4" hole near the bottom. With a threaded ball valve and some flexible 1 1/4" tubing (like Home Depot sells in plumbing), you can drain water very easily. In California, I just drained water to the yard (under the garage door). In my basement fishroom, to a floor drain. Cover the drain hole with some cross stitch backing to prevent fish from getting sucked out.
Filtration is easy: I've used air-driven boxes and sponges, canisters and dumps.
I heated with room temp and/or a heater sticking through a piece of styrofoam. I've also just had the heater stuck to the bottom of the tank with suction cups. It didn't melt it.
Back when I kept African cichlids, I had colonies of peacocks, haps, Lethrinops, etc. in bins. A little PFS on the bottom and PVC condos work great and ease catching the holding females.
I kept Africans (mbuna) outside in our (200-300g) goldfish pond when we were in Sacramento. It worked OK but I didn't see any miraculous growth or colors or anything. They hid a lot in the plants but got along with the goldfish.
Matt