Water Change Routine

Water changes are a pain on a larger system. In my case this is simply because of the quantity of water that I need to change. I have a 240g DT and a 75g sump. My water change practice currently involves using a 55g brute can (on wheels). My ro/di unit is in the same room as my tank, which is the front living room. So essentially I have the can sitting in my living room for a couple of days while I fill it with ro/di water and then mix up my saltwater. I then use a PH and pump water into a 5 gallon bucket and make several trips back and forth to the toilet as I drain the sump. I usually empty 7 buckets. I then fill my sump from the brute can. I usually have a 5 gallon bucket left over that I keep on hand for adding to the tank as necessary (skimmer).

I would like to keep large volumes of water premixed but just cannot seem to dedicate anymore real estate in the house or garage for my hobbies. I have all my aquarium stuff, and a gun/reloading room. My wife wont put up with anymore areas of the house being "taken".

So my question is how do you guys store your water and what are your water change procedures? There has to be something I can change to make this more efficient.