I've heard about those bags clogging up very easily, is this true?

well not really, they have larger surface area than a ceramic filter and larger pores. Generally not an issue with reasonable clean water.

I did manage to clog mine millbank once, but that was with muddy water from a car track in the forest. I also had to clean out mine MSR miniworks 8 times that day, filtering that water, with a fine towel on the inlet...

PC2K, could you tell me what the dimensions of the Milbank filter are, and how long it takes to filter a specific amount of water? I would like to try to make one. Thanks.

Sue

well they come in various size's and the rate the water flows is depended on the size of the bag and the quality of the water. The size on mine is: 20cm wide and the length on the long side is 44cm and the shorter side 33 cm. ( i only do metrics's, no ruler in sight with inches on them)

Never really measured the flow. With tap water, usually a slow stream of water. The bigger models are faster, than the smaller ones. With mud from a car track, this will slow down to a drop every 30 second until the millbank is totally clogged up. The drops however where 100% clear looking.

According to the University of Rhode Island, coffee filters have a pore size of about a hundred microns. (http://geo.uri.edu/skydust/faqs.aspx)

Depending on what you mean by big contaminants, a coffee filter might work. If I ever have to use my ceramic filters to purify water, I certainly will pre-filter the water that goes into the reservoir for the ceramic filters. I'm not sure I'd use a coffee filter, but I'll use a strainer of some kind.

Okay, that's about 17.5"L x 13"W with an 8" diameter opening.

That sounds like three bags out of a half-yard of fabric. Plus the hanging handle.

Thanks!

Sue