Between Ben's idea, Dale's idea, and the fact that I had all of the necessary components handy, I felt inspired to rig a pre-filter for my upcoming trip around the TRT. I used a Steripen throughout my PCT thru hike last summer, and there were a few lake sources in OR that had some little red critters who met their demise in my gut -- which, while obviously it didn't kill me, I would have preferred to not ingest them. I love my Steripen, it worked flawlessly for five months -- but a "just in case" pre-filter would make it even better! So here is my first ever DIY gear attempt!! I'm pretty pleased with myself :)
I used a FoodSaver quart bag, cut a tiny slit into the corner, and inserted a Coghlan's fuel filter that I cut down to just the bottom bit. I then used a heat gun on the low setting to melt the bag to the plastic. It works!! A finger over the spout easily holds the water in, and I can scoop up water with the open end -- at least in theory, as I haven't trail tested it yet.
At half an ounce, and about $2 (assuming you have a heat gun handy) and about three minutes to make, it'll ride along in my pack this summer! Thanks guys!!