Tony
I posted a design for a gravity filter several months ago on this site. The discharge hose was about 3 feet and it did not require priming (except for the first use after changing the filter).
I have a quick connect for a camelbak on it and using the additional height it will develop enough pressure to fill the bladder without opening my pack. Surpisingly I have found that the filter cartiage last long than it did in the pump. I used it on the AT last spring and it was a big hit with everyone that saw it at work. No pumping, no waiting for chemicals. Just fill the bag and start drinking.
The name of the post was "Light and Easy Water Filtration for the Lazy Backpacker". It is on page 5 of this forum.