Camel

I have a 1.8 or ?2L Playtypus bag with hose+bite valve. Rolled up it takes up minimal space. I melted two holes through the extra plastic at the base, and ran some utility cord through them. I can then hang it up (at camp say), and use the hose/valve for a mini shower, clean stuff, fill stuff etc. I've rarely needed to ride far with it filled, but it seats nicely strapped across my rear rack under my tent. Has held up for me for ?3-4 years so far.

I only put water in it, and I give the whole system a good cleaning/soak in dilute bleach at home when it gets "funky". For cleaning on the road/trail, I add double water treatment tabs (non iodine-teeny Silver ion ones), let sit+rinse.