Camebak has recently made available a retro-fit kit for their HydroLink quick-connect/disconnect & shut-off valve fittings. It includes an adapter for the end of the fill tube from a water filter. To use, one unplugs the mouthpiece, makes sure the valve is open, plugs in the filter output hose, & pumps away.

Filling in less than optimum conditions (or even optimum for that matter) was one of the reasons for the introduction of the larger-opening of the Omega reservoir. Though I don't carry one (yet), it seems to me that a sponge would be quite useful in the scenario described by wazza (filling from a seep, tree hollow, etc), as would the intake hose of a filter, if carried.

Just my "tuppence", as our friends across the pond say.

David