Jerry, I just plan to use one bag (for dirty water), and filter directly into my water bottles.
I think my gravity filter setup, everything included (water bag, tubing, valve/clamp, fittings, filter, etc.) might turn out to be in the same weight neighborhood as the Sawyer squeeze.
The filter is a Barnstead inline polyethersulfone hollow fiber filter, exactly like the Sawyer but smaller. Despite the smaller size, with 5 feet of tubing above it, the filtration rate is plenty fast. I've tried it twice and it took 77 and 71 seconds to fill up my 1 liter bottle. Like the Sawyer, it will filter millions of liters of water, and only require occasional backflushing to keep it clean. The tubing is thin-walled polypropylene rather than the heavy vinyl tubing that many gravity setups use. The tubing is tough but collapsible, so the filter has to go at the bottom. I attached a threaded cap to the filter so it screws directly onto my platypus bottle.
I just ran some water through it and then weighed it. With everything (filter, fittings, clamp, and five feet of tubing) except the water bag, and wet, it weighs 1.4 oz. It is right around one ounce when dry, I think. But it will be carried wet, so I think, for water filters, wet weight is more relevant than dry weight.
With a 2L silnylon or cuben water bag, the whole thing should come in under four ounces, I think. The fittings are arranged so the tubing can be removed and the bag can be attached directly to the filter, to function like the Sawyer Squeeze if I don't want to wait for gravity.
So, I think it would be clever to use the water bag for other things as well, and I'm interested in any experiences that anyone has had using their gravity filter water bag for other things, and what, if anything, they had to do to it to make it functional for other uses.