wall 14 to leave a respective exit opening 28 between the end of the baffle and the adjacent side wall a simple centrifugal pump impeller 30 is mounted in the central portion of the sump over an inlet opening 32 fig2 in the bottom of the sump the impeller is mounted on the lower end of a vertical shaft 32 which is turned by a suitable conventional means not shown the impeller is spaced slightly above the bottom of the tank and includes downwardly and radially extending blades 34 welded to the underside of a horizontal disk 36 secured to the shaft thus the disk of the impeller and the bottom of the tank act as a pump casing for the blades as the impeller is rotated oil and water are drawn up through a supply line 37 connected to an inlet 38 in the bottom of the sump mixed and pumped outwardly from the sump into oppositely extending retention channels 40 formed between the inlet end wall 16 and the baffle 24 mixed oil and water in the retention channels flow away from the impeller and out the openings 28 at each end of the baffle and is uniformly.