Flushing Is Not Just a City in New York State

In a post-apocalyptic world in an improvised shelter in your home, some large office building, or big box store, keeping the toilet running matters.  If you are on city water your city water tank gives 0.433 psi per foot of elevation.  I suspect most cities have pressure regulators to keep this pressure within reasonable bounds.  

Where I grew up in Santa Monica the water tanks were at the top of a 300 foot hill on the northeastern border.  The story of Santa Monica water is the story of Los Angeles using access to the Owens Valley water to lure cities into consolidation.  I was told that Santa Monica went so far as using 220V, 50 Hz power until WW2 to make Los Angeles' blandishments unattractive to residents.

Anyway, what if you are not on city water?  You may be relying on a booster pump as is the case for many of us on wells.  You can fill the toilet tank with urine.  You are supposed to drink 2.6 liters (for men) and 2.1 liters (for women) per day.  Some of that will be in your canned food.  Some will be lost in perspiration and transpiration, but most will go through your bladder.  Use it to fill the toilet tank as best you can.  For men this should be easy; for women, a bit clumsy.  I doubt this will give you many flushes per day, but you will probably be eating little and moving around less, so the number of required flushes will likely be small.