I had something like this in mind:
http://www.eastman.com/Company/News_...ter_300dpi.jpg
with the internal filter removed and inverted.
As for the dirty water reservoir, we have some 10L olive oil containers, they are thin walled but they are free so i intend on using some of those.
http://tekmetalambalaj.com/images/ze...tenekeleri.jpg
The can be disposed of and the cap used for later on. I kind of fancy the idea of placing 10 or 20 liters at once and get 1000km's worth of water in on go.