I agree with all that you say but I expect any city in T2K to be more or less like Harare except of course if it has some kind of ruler (assuming he is competent).
I also expect people to grow more resilient to eventual disease. Don't forget that these people already survived several (cholera, plague, flu...). If you could bring someone from the middle ages to our time he would die in no time. The fair point with this is that if you could be brought back to the middle ages you would die as fast (disease, lead, polution..., name it).
Whatever, when things go as sour as in T2K people start to care about the instant and, in most of the world, no one would be around to put up what you suggest. However, if you have that knowledge, I'm sure you'll use it for the better. In addition, these solutions might become more common when things start to settle down and in the most organized areas (in the parts of UK under HMG's control for exemple).
For flushing your toilets with 2nd hand water you don't need any complicated device. Just throw about 20 liters of water in your toilets from any kind of can (or tank) and it's flushed. I do that with the water I collect from the dryer and it works fine. I'm not really an ecologist but that is 20 liters that won't go on my bill and I have to throw it away, so.
Anyway, if I was living in T2K I would simply dig a hole in the ground, put some kind of chair above it (+ some kind of colth for a little privacy), and when it start to be too stinky, I'll cover it with dust and start digging a fresh new hole. If I'm lucky, I'll be living next to a river and do everything right into it. If it's too cold outside or if I live in a city, I'll fill up the tank and throw it by the window on the dreaming pedestrian walking outside. Just to bring him/her back to the nice and happy reality of T2K
