I've been using a waterproof dry bag from Cabela's for several years now (think "reverse" use of a dry bag).  It only takes an instant to fill out in the lake (although getting it back over the gunwales is a bit like landing a whale), I dispense water via the air-bleed valve and I either drape it over a log, rock or hang from a tree as a "dispensing station."  It also dumps easy when clearing camp and rolls up into a relatively small space that I can stuff.  After the trip, I can turn it inside-out for cleaning.

Only downside so far ... you have to be a little conscious about poking a hole in it.  I've not had that problem, but I know my paddling partner's "sprung a leak" on one trip.  He has also used his as a shower on a trip or two.

dd