the bath liquid 30 is brought up to the outlet 52 from the spinneret by creating a vacuum in the tube 20 which draws the bath liquid up through the vertical tube 20 to the outlet 52 one way of accomplishing this is to evacuate the tube 20 through suction line 42 that passes through the piston 40 and is suctioned through pump 44 an appropriate valve such as a float valve would prevent the liquid in the tube 20 from being sucked out another technique for filling the vertical tube 20 is illustrated by a comparison of fig1 and 2 initially before the hollow fibers are extruded the piston 40 with the spinneret 50 installed is at the bottom of the tube with the exit 52 below the top 28 of the liquid bath fig2 the piston and spinneret are drawn to the top of the tube e g by a drive mechanism fixed at one end of the piston since the piston is sealed on the wall of the tube and the wall of the tube 20 has a substantially constant cross section over its height raising of the piston draws a vacuum in the tube beneath the piston and that vacuum is filled by bath liquid drawn out of the vessel 12 this method also has the advantage of being easier to start up i e the fiber extrusion process can be established while the spinneret is in the lower position where it is accessible to an operator should there be an upset in the start up operation once the fiber extrusioin process has been established the piston spinneret can be drawn to the top of the extension tube from which fiber production is conducted it may additionally.