settling in the tanks 3 and 5 is continued until the purified oil removed through the conduit 27 contains not more than 2 weight percent of water and solids combined preferably settling is performed for a period sufficient to provide purified oil containing not more than 1 weight percent combined water and solids preferably the contaminated oil is settled in the tank 3 for a period sufficient so that the partially purified oil removed from the tank 3 through the conduit 19 normally contains from about 2 to about 5 weight percent combined water and solids the intermediate layer 13 in the tank 3 is removed and passed through a conduit 29 into the tank 7 the intermediate layer 23 in the tank 5 is withdrawn into a conduit 31 or could be withdrawn with the bottom water phase to tanks the material in the conduit 31 may if desired be passed directly into the tank 7 or directly into the conduit 29 by means not shown through the conduit 33 which is equipped with a valve 35 preferably however the valve 35 is normally closed and the oil cuff layer material in the conduit 31 is normally introduced into the intermediate layer 13 in the tank 3 the material entering the tank 7 is settled to form an upper layer 37 containing oil and from about 5 to about 80 weight percent combined solids plus water and a lower substantially solids free water layer 39 the water oil solids.