mastertangler wrote: ".....when you are hanging your "dirty water" bag try and get into the habit of resealing the ziplock seal shut. My tendency was to leave it open and after hanging it from a limb pieces of bark would invariably find their way into the bag due to the strap rubbing against the bark. Any material dislodged falls straight down into your bag."

I've been using the Platypus system for four years now and much prefer to leave the "dirty water" bag open.  I backflush and dump regularly, so anything that might drop into the bag gets tossed.  But I do seal the "clean water" bag and leave it that way, specifically to keep debris out.