Thanks for all the responses. I think we're on to something here.
Paul / LiveTicker - Some of the things you mentioned, like the threads you refer to, talk about loading water into the TM using a pressurized source. I'm talking specifically about loading water from a non-pressurized source, like a 5 gallon jug. I wouldn't be doing this at home, but out in the boonies where I have to drive a few miles to get water and bring it back to camp.
I like your ideas with the valves, but I'm trying to stay away from valves if I can. In my 2720SL, there is barely enough room to shine any light under the sink where the water tank, pump, water heater, and accumulator all reside. Not only would having a valve-free solution be simpler to operate, it would also mean I don't have to enter this dungeon every time I want to load more water. I definitely do not want an electrically actuated valve. Way too much hassle and expense and it's just another thing to break.
Bill - Glad you like the idea! You might be able to get a pump of a different brand for less.....one feature on these pumps is the pressure switch, and obviously that is not required for this application. Perhaps one that does would be a bit cheaper. You definitely want to be sure whatever pump you do buy is self-priming though and is safe for potable water.
Here is the same above above for $63 delivered (the one above charged more for shipping):
http://www.amazon.com/SHURflo-2088-4.../dp/B0006GK5NA
The one above is 2.8 gallons/min, and I personally wouldn't want to go any slower. But if you want to save a few bucks, this 1 GPM pump is $45 delivered....it doesn't have a pressure switch, but I would want to confirm that it is self-priming:
http://www.amazon.com/SHURflo-100-00.../dp/B00074QU6C
ThePair - The outside shower hose or plumbing is not utilized at all in my current method in loading water. In fact, I do not even have an outdoor shower. I use an additional Shurflo pump, identical to the factory installed one, and simply connect to the pump two 3-foot lengths of hose I bought from the hardware store. One hose goes in the water container, the other hose goes into the fresh water tank fill hole. I connected a cigarette plug to the power wire for the pump, and with the pump outside, I snake the wire under the velcro flap and plug it into the socket where the antenna pre-amp is on the fridge wall.
You'll want to be sure your vent hose is connected. If you overfill your water tank, water will eventually start coming out that hose....and it sounds like the way yours is now, it will make a mess under your sink.
I took a look under the sink yesterday afternoon after starting this thread, and I don't see a good spot to install a new city water flange. Looking under the sink, the water tank fill and existing city water flange are one on top of the other on the right in the space above the tank. Directly to the left of that is the water pump, and to the left of that is the water heater. There is some free space UNDER the water heater, in between it and the floor, but my guess is there is framing in that space to support to water heater. But even if there isn't, because there is such a small space in between the water heater and the edge of where the flange would go, I don't think that's a good place. I don't want to weaken any support for the water heater.
So for us lucky 2720SL owners, I think more creativity is required. A few ideas:
1) run the pump inlet through the floor, and the connect an elbow under the trailer to run it to the side of the trailer. So far, this is my preferred solution.
2) use the existing city water flange -- use a Y to connect the inlet, and a check valve (which requires no actuation) to prevent the aux pump from sucking water out of the TM plumbing when you are loading water. On the other hand, perhaps no check valve is needed. If all the faucets are closed, no air can enter the lines, and the pump will instead be pumping water from the water container.
In any event, the problem with this solution is that when you connect pressurized water to that flange, I think it will go right through the pump, and you will start filling your water tank. I may call Shurflo or experiment to confirm. EDIT: I just talked with a tech at Shurflo, and confirmed that the water would go right through.
Need to think about this more......I'm not sure how to fix this without a manual valve.
3) remove the existing fresh water fill flange and replace it with a new city water flange to connect to the aux pump. To fill the water tank from a pressurized source, connect a hose thread adapter to the drain under the trailer. This won't work for me because my drain tube is pinched by the tank, severely restricting flow. I can't fix this without making a new hole for the drain, as the tank is already over towards the fridge as far as it can go.
Dave