Abstract: Apparatus for conveying a viscous liquid from a tank through a supply line to a device to be supplied with such liquid and thence to the tank via a return line, the liquid being heated either in the supply line or in the return line, or both. The apparatus includes concentric conduits extending into the tank and establishing supply and return passages connected respectively to the supply line and the return line. The conduits terminate at different levels inside the tank and the shorter of the conduits carries a sleeve at that end which is inside the tank and which is adjustable from outside the tank so as to vary the effective length of such conduit to enable the lower end of either conduit to extend beyond the lower end of the other conduit.