I'll have to defer to the details in Rick's reply, but I'll add that it's pretty easy to set up the Britta to be as a gravity filter. The 1L flexible plastic "canteens" I use have a decent flow rate when used them this way.

I've not really filtered any murky water with them. I always get my water from clear streams or springs here, but I'd certainly give it a shot if I were you, and if you do I'd be very interested to hear how well it worked for you.

As I recall, Britta claims these filters are good for up to 50 gals of water. So, I'd think that it should do pretty good at filtering 5-10 gallons of water that was pretty muddied up, which should be more than enough for most trips and keep your Sawyer much cleaner.