the individual trays 42 of the illustrated embodiment includes several compartments 44 that hold agitating elements that move and thereby vibrate the solids deposited on the screen panel assembly 16 the agitating elements although not shown may for example and without limitation include balls made of metal plastic or other suitable material and are held within the compartments 44 the agitating elements are supported by a bottom support screen 45 and confined in the compartments 44 by partition walls 47 defining the compartments 44 it is contemplated however that an alternative agitating structure may have other shapes and or include any number of trays other than the two trays of this exemplary embodiment such alternatives include without limitation an agitating structure having a single tray rather than a segmented tray assembly referring to fig1 and 2 exemplary screen panels 20 22 according to one embodiment of this invention are shown each screen panel 20 22 is substantially identical to each other the frame 26 of each screen panel includes the downwardly turned lip 46 extending longitudinally on each lateral side edge of the screen panel 20 22 the lip 46 includes the tabs 52 53 the tab 52 has a generally sloped leading edge 58.