How does the Lara drain-down button work? The Lara drain-down button facilitates the draining of thermal fluid back into the circulator. When the button is depressed, air is allowed to enter the circulator system through a gold-coloured filter situated above the button. This makes the draining process much faster. You would first need to ensure that the circulator has enough space in its expansion tank to accept the oil. (An additional external expansion tank can be added to a Huber if required.) The circulator would have to be positioned below the Lara, as gravity is used for drain-down. To drain the Lara vessel jacket: Switch off the circulator. Press the ‘drain’ button on the left hand side of the triangular Lara framework. The button must remain depressed to completely drain the jacket.