I was out at Philmont this summer...
I carried:
1 L Nalgene
2 L Platypus bladder
3 L Platypus bladder
and a pump filter.
Neither of my platypus have the zip opening -- just the screw on fitting for the hose.
I found that I could remove the bite valve and plug the hose into the filter to fill the bladders.
The upcoming days water outlook determined which vessels I filled.