A used Katadyn mini water filter, a compact unit designed to fit in large pockets or rucksack pouches. I think these units have been discontinued now.
Katadyn Mini Water Filter
Katadyn Mini Water Filter, Bushcraft, Camping, Travelling
Katadyn Pocket Water Filter, New Micro filter Endurance Series
Katadyn Replacement Water Filter SteriPEN FitsAll and Pre-Filter
Katadyn Pocket Water Filter Survival Camping Tactical Outdoor Black
