Patent ID: 7211225

Claim:
An apparatus comprising: a sample chamber for holding a sample suspension, said chamber comprising an opening for receiving a sample suspension, an outer wall, and a filter support comprising a first step having a first depth from said opening, a second step having a second depth from said opening that is greater than said first depth, and a third step having a third depth from said opening that is greater than said second depth; a first vertical weir extending a first distance from said first step of said filter support, said first vertical weir, said outer wall, and said first step defining a first sub-chamber; a second vertical weir extending a second distance from said second step of said filter support, said second distance being less than said first distance, said first vertical weir, said second vertical weir, said outer wall, and said second step defining a second sub-chamber, and said second vertical weir, said outer wall, and said third step defining a third sub-chamber; and means for drawing the sample suspension through a filter mounted on said filter support.