Seems these HDPE bottles might be a good answer to backflushing a gravity filter like the MSR autoflow (due to SQUeezabiLITY). Anyone have direct input? Thanks.

Gravity is a force, and a gallon of water weighs in around 7lbs through an orifice builds up a little bit of pressure. But I should have used the word "gently" before. It really doesn't matter, it doesn't work well. I went ahead and got one of these bottles (the wide mouth version) and the fact of the matter is that you simply cannot squeeze the bottle enough to make it worthwhile for back flushing. Inevitably vacuum builds up inside the bottle and you have to loosen the cap ever 100 mL or so. A minor setback. I still like the bottle, but It seems I will need to trade out my camelbak for a platy or msr bladder that the bottle adapter will fit in order to properly maintain my filter in the field.

Like it states, gravity filters work on the gravity principle & by forcing water back through, as you stated by squeezing this bottle to backflush, could result in damaging the cartridge. I have the Platypus Cleanstream & perform backflushing by pouring clean water through a small funnel back through the cartridge until it is clean & running true. The reason I use a funnel is because I removed the clean water bag to reduce weight. (See my review.)