WB, I think ... but I admit I'm totally not sure .. I think the brute is only used to hold water to get ready for replacement. I don't think it holds water all the time. Again, this is just my doing the I think this is what this does, I think the autofill is so that he can turn the water on to fill the brute up to the amount that will be used for a water change. If I'm seeing this right, the autofill is insurance against the tub overfilling with the water turned on. Then the brute tub is treated for decholorination, and used for a water change. Then it will sit virtually empty until the next water change.
My very first rain barrel is a rubbermaid, not even a brute. Cheap way to prove to hubby that it was worth it to invest in water barrels for rain water collection. It just went through it's third year. I totally did not expect it to last a single rainy season. But it is on the north side of our house and gets no sun light, and the water level waxes and wains; so I guess that tempers the stress somewhat. But yeah, if I had the funds I would use a barrel instead.