I have so many questions.... However, I'll make a suggestion instead. Go to the hardware store and buy a couple of buckets to fill instead of the bottles. Should be able to get a few flushes out per bucket and it will be easier. The biggest question I have is why has this water leak not been repaired in so long that there is an alternative toilet flushing protocol. Most places would just ask a neighboring business for access to their restrooms if it was only going to be a day or two.

A new roof on my house.

I live in Florida and absolutely use this principle. Once I have to start having to run heat, I start cooking a bunch. I'm talking about baking bread, roasting pork butts, large stock pots of gumbo and running my antique tube radio all the time. During the summer I actually run the toaster oven and air fryer outside because they are so expensive to pay to heat and cool at the same time.