Abstract: A preferred cap for the fill spout of a water bed comprises a screw cap having a top and a threaded flange which is capable of mating with the threaded portion of a fill spout, a turning knob, and a sliding shaft for connecting the screw cap to the turning knob. The shaft allows the knob to reciprocate between a first position substantially abutting the top of the cap and a second position raised above the top. In the raised position, turning of the knob turns the screw cap through the shaft, thereby unthreading or threading the screw cap onto the threaded portion of the fill spout. The knob may also be used as a handle to apply sufficient force to extract a retracted fill spout from its stored position in the envelope of the water bed.To enhance sealing of a cap in a water bed, a sealing thimble may be used to fill the inner volume of the fill spout. An outwardly projecting flange of the thimble bears against the rim of the fill spout.