I have to assume you're using some kind of tubing to hook up the outside shower hose to the tank fill/inlet port. What have you found that works, or is this all a thought experiment right now (which I love, BTW)
I'm still looking for a solution, as my current one leaves a lot to be desired
Utilizing the existing pump sounds quite nice, I'm just thinking that, perhaps, running a short internal hose might not be better than trying to rig something up to the outside shower (involving removal of the shower handle to use, etc). It would be a little more like your first plan for that portion of it, but use-wise and installation-wise it seems like a little less hassle?
Since the city water fill pipe has a cap on its end, and I have never had anything come out of my "vent pipe" in the water tank -- in fact it's not even connected to the outside properly, just floats near the vent screen -- I'm thinking that hooking that little hose directly to the city pipe with a valve would work. The pump would fill the tank through that air vent hose just fine, and if you were filling the tank the "normal" way, you could just open the city port to vent air, if needed.
Looking under the sink on my 2720SL, even with the tight fit, I think that wouldn't be too difficult to manage.
I think this is an incredibly clever line of thought. With a little more imagination, one could conceive of using the city port for the fill connection, rather than drilling a new port, and diverting the water from there through the pump and then back up to the tank in a retrograde fashion.
If one could find a compatible 4-way crossover switching valve, this could be done with a minimum of fuss. Just install it between the city fill line and the pump intake, and a simple twist would make it all work.
So that begs the question: anyone know of such a beast? The only thing I've found so far is:
http://www.evsco.com/4-way.htm utilizing a "double L crossover" pattern. Assuming the polypropylene is considered safe for drinking water, this would then allow a simple installation, labeling the 4 ports as such:
A. City inlet
B. Tube formerly connecting A to the high-pressure side of the system (i.e. pump outlet)
C. Output line from water tank
D. Input line to pump.
In the stock TM, A & B are connected as one tube, as are C & D. This valve would, with a twist, swap the connections so A & D are connected, as well as B & C. Thus, water would come in through the city connector, into the pump, out into the high pressure system, and then dump via B into C, which leads to filling the water tank. Once filled, a simple 90 degree twist would set things back to normal operations. This carries with it the simplicity of a single twist on one valve to convert from one function to the other, and it makes it more or less foolproof, since you can't forget to open/close all the needed valves to switch modes. It's either normal mode, or fill mode.
Anyone think that would work?