https://www.campcraftoutdoors.com/product-page/pre-filter-for-grayl
TO prefilter water while we are out hiking or camping ai always a good idea. The GRAYL water bottle is a very good camping / hiking water filter system. When we add a pre filter bag we reduce the clogging of the grayl filter ctg. and get more use between filter changes. in this video i talk of was to use a pre filter with the grayl system