Abstract: A rotatable combination that includes first and second members respectively having first and second longitudinally extending pluralities of splines. The second plurality of splines extend substantially parallel to the rotational axis. The first plurality of splines includes first and second longitudinally extending sections having different orientations with the second longitudinal section defining an angle with the rotational axis. The first longitudinal section engages the second plurality of splines before the second longitudinal section during assembly of the two members. Engagement of the second longitudinal section with the second plurality of splines generates a greater resistance to longitudinal movement than engagement of the first longitudinal section with the second plurality of splines.

Abstract: A septic tank system including a tank and a downstream fluid system. The tank is adapted to receive sewerage and discharge liquid effluent into the downstream fluid system. A treatment chamber is located in the downstream fluid system and receives an ultraviolet light transmitting device which is removably insertable into the treatment chamber. A photoelectric device can be positioned in the downstream fluid system proximate the ultraviolet light transmitting device to monitor the operation of the device.