top free edge of the tank walls 36 38 the wing screws 138 are threadedly engaged with the overhang portions and the tank end walls to secure the filter units firmly upon the manifolds a foam rubber or plastic strip 146 is secured to the longitudinal underside of the medial web portion 140 to engage the upper edges of the filter units 14 and hold them more uniformly in parallel spaced apart relationship when filter units require replacement or maintenance they can easily be removed and replaced without tools by disengaging the wing screws from the tank end walls and merely lifting the hold down bars out of the way the polluted liquid input trough 24 comprises the outer side wall 152 end walls 154 154 and a bottom wall 156 the discharge end 158 of the input conduit 74 discharges the polluted liquid into the trough 24 from which it passes over weir 76 onto the liquid distributing plate 48 that extends the length of the tank between the front and rear end walls 38 36 respectively the overflow trough 26 outboard of the tank 12 as is the input trough 24 comprises an outer side wall 166 end walls 167 167 a bottom wall 168 a downwardly tapering funnel portion 170 and a discharge conduit 172 at the apex of the funnel portion to receive and discharge solids and liquids that overflow the weir 174.