Abstract: Flushing liquor from a gas main of a coke oven is fed into a preliminary gravity separator to provide an aqueous liquid phase substantially free of tar and solids for reuse as flushing liquid in the gas main. A tar phase obtained from the preliminary gravity separator is fed into a circuit including a centrifuge for three-phase clarification and separation. The circulation in the circuit being at quantities greater than the quantities of the tar phase introduced per unit of time from the gravity separator to obtain a tar surplus which is substantially free of aqueous liquid and thick tar. The tar surplus is removed from the circuit by feeding clean tar from the centrifuge into an overflow tank from where clean tar is reintroduced into the circuit and clean tar is returned to the preliminary gravity separator in controlled response to the tar level therein.