Cobweb
Before you judge the buff as not good as a strainer try this trick
Take one end at four points, seperate them as in north south east and west.
Take the material at NE, SE, NW, SW and place them back in the centre. If you have womens hair pins this is considerably easier, or 2 paper clips.
Twist the N,S,E,W sections each, 360 degrees. clockwise or anticlockwise doesn't matter, just do all four the same way.
Crown the twist braid strands.
Crown again
This is tight and tricky to do but works like a charm.
It's obviously not as thick as a millbag for filtration, but will remove the larger particles quickly enough. Especially if topped up with sand, mosses etc.
If you are unfamiliar with crown knots, just google it, there are hundreds of demos, pictures and even animations.