Exactly ... it is one big thing I miss about running smaller tanks!!
In the scheme of larger tanks my 280g is on the smaller side but I am still unable to do anything larger than 50g at time. I could maybe bump it up to something larger if I did a 50g changeout in the DT and then empty the sump and then use *it* as a second mixing chamber but I don't like to use water that hasn't been mixing for at least a few hours.
Buddy of mine on an acreage has something like a 1000g rain barrel (thing is massive!!). Something like that would be awesome to have onhand but there's .. kind of not a lot of options to put such a beast.
Wish I had thought to sink one of those in the ground under my deck before I built the deck and then just build that sucker around/on-top of it.
Next house maybe for sure!