What baffles me about the Sawyer filter is the ambiguity regarding backflushing. The instructions have an advisory that says something to the effect, "Do not reverse the flow of the water." Do they mean, "Do not run dirty water in a reverse direction," or do they mean not to backflush clean water through the filter. Certainly, they can't mean the latter, because they mention using the faucet adapter to backflush. However, my question is this: Can/should you backflush it in the field (like the Platy Clean Stream instructs), or should you wait until you get home to your faucet?
Also, is there a test you can do to make sure the filter is working properly? On the instructions for the Platy Clean Stream, it says to try to blow bubbles through the filter in a backwards direction. I tried this on the Sawyer, and air seemed to pass through in the reverse direction. Is this bad?
Regarding your question about the convenience of the Sweetwater pump system vs. the Sawyer gravity system, I guess it comes down to two variables: a) flow rate and b) prep time.
Let's discuss these two variables in turn.
a) The flow rate of the Sawyer seems good now with tap water, but I don't know what it would be like after 1 month of thru-hiking. Also, the ambiguity surrounding whether you can backflush in the field exacerbates this. Is backflushing in the field OK? Will it improve the flow rate of the filter back to original specs?
The flow rate of the MSR Sweetwater, on the other hand, is not contingent on the filter itself but on my own muscle. If it slows, I pump harder. Also, it is field-cleanable with the brush provided.
b) The prep time is undoubtedly longer for the gravity setup. Filling your dirty bag will take time. Even a 4L Platy water bag with a zipped top will only accomodate about 2L maximum before you have to top it off with another scoop container (don't forget to factor that into the weight of your system). If the water source is really shallow, you will have to scoop and pour most of the water. If you have a deep pool or a running stream, this will probably reduce your prep time. You also have to find a place to hang your bag, which involves rigging some cord for this purpose. Sure, you could stand and hold it, but you would have to stand pretty high to accomodate the 30" length of dirty tubing between the dirty bag and filter and then some to accomodate the clean tubing.
With the pump system, you just place your dirty tubing in the water and pump away. Even shallow streams can be pumped successfully.
Last but not least, the Sweetwater has a carbon element to improve taste.
I think will do some experimenting in my backyard and time the prep-time as well as the flow-time for both filters. I will place water in a bucket-like container to mimic a water source. Then I'll come back with some data.