I think they were using bandanna as the prefilter on MSR Ceramic. It helped but still let in a lot of fine silt that required frequent cleaning. The river water was pretty churned up and muddy back in March.
The coffee filter is a good idea. :sombrero:
Just this morning I threw my canyon shoes and neoprene socks in a bucket and turned the hose on them. I got more than a few tablespoons of silt left over from my trip. Your son must have had enough for a few sandbags that he washed out! :elkgrin: