For anybody who thinks that my plumbing is going to be problematic, I can prove that it won't.
There are three pressure-fed regions in the Fortress. The pump tower brings up water with five pumps. The pumps take in 5*7 maximum water per step. The water then flows down one tile wide tubes until it reaches the waterfalls, which widen to 3. The waterfalls will split the water into two tiles of 2 and one tile of 3 per step. The fifth central waterfall (which is new) is only 1 tile wide.
The water then drops down about five z-layers, cascading through my dining room (three story), and into a redundant drain system. First, it falls into the cistern, filling it. The cistern should hold an obscene amount of water, and can be drained by opening the floodgates by the obsidian farm.
When the cistern fills completely, the water will then begin to overflow into tunnels above the cistern, which lead into the royal quarter's magnificent pond. The tunnels converge, forming a width of 3. Meaning, 35 water per step flows in, only 21 water per step can move. This means that the tunnels will fill faster than they drain. This is intentional. There are three pumps above this tunnel, which mitigate the pressure, safely feeding the water into the royal quarter's supply. I have not devised a way to drain the water... Yet... These pumps, however, will NOT work unless the cistern is full, and the royal quarter's intake tunnel is overflowing (which it always will be unless of course the cistern is empty).
This is where the third backup comes into play. Two layers above the royal quarter's intake, There are drainage ditches with widths of 3, 3, 3, 3, and 1. These ditches meet seven waterwheels inside of my tower cap farm, and seven pumps. These pumps will turn on. There is also a large bridge structure in the tower cap farm that will allow me to flood the farm. Note that the pumps DO NOT block the drainage tubes below.
The Farm is HUGE, and will take some time to fill, but once it is full, the pumps will stop, I can pull a lever, and open the releases, which open floodgates. These floodgates punch into the end of the drainage tunnels, allowing the water to be removed safely. When these floodgates are open, no new water will flood in, as the floor hatches that stop the waterfalls will swing shut. That way, even if the drains back up, my fortress will not.
There are seven more waterwheels in the end of these drainage tunnels, which are fed absolutely last. This fuels my hospital's water supply with a way to depressurize from the cistern. The cistern is so heavily pressured, that I cannot use it for anything other than making obsidian, so I have installed another redundant flood tunnel much like that of the royal quarter, which will pump water safely into the hospital so that I can help cure, and help kill the patients.
The hospital has its own drainage system, which can be controlled independently for each room. The cistern will actually refill faster than a room can drain it. Again, 35 water in, 7 water out. However, if I were to kill off five or more patients at a time, it would drain very quickly.
Note what I said earlier about the main drainage tubes, and the pumps that allow me to flood the tower cap farm. the water will flood past the pumps if they are off, and the pumps will redirect the water and create another small waterfall if they are on, so really, there is absolutely no chance of flooding anywhere in the fortress... I hope...