It really depends on what type of wood the sawdust is from. There are 7 woods known to man that have a density of over 1.00 g/cm3. (the density of water) If you have any one of the remaining types of sawdust, you can probably just shake the mixture to make all of the sawdust float to the surface and just scrape it of the surface with a net or capturing device.
(Different person)
I do science and we just recently learnt how to separate mixtures, and to separate sawdust from a mixture you need to use the technique called "filtering".
filtering: Suspended particles are trapped on the filter paper forming residue. The smaller particles pass through the filter paper forming the filtrate.
meaning the sawdust would get stuck in the filter paper whilst the solvent(water/liquid) would pass through the paper.