You CAN field backflush, but I've found that the best way is to rig a second hose w/quick connect &, basically, decided it's instead easier to just run the prefilter. I forget exactly how far I got last time before the flow rate got annoyingly slow, but I think it was around 6 days filtering for 2.
My field backflush set-up used another hydration hose/fitting, quick connects, second platy. Hook up for reverse flow, sometimes stand on platy to generate enough pressure for backflush. Usually not needed. Or I could eliminate the extra components.
For shorter trips could probably do away w/backflush and prefilter, BUT since my water source is filled straight from the river and has all the included floaties (leaf detritus, etc) I figure the prefilter is easy, not a big weight issue, & might save me a little headache.