My reply was regarding winterizing - to pull the drainplug (beyond the shutoff), getting rid of the last bit of water. Then freshwater rinse, let that drain and call it good. Probably the hose at the pump would also need to be disconnected to make sure it is dry.
Still leaves us with the slow drainage issue. What about replumbing with a full size shutoff, elbow, coupling and cap - eliminating the pump altogether? Yes, it would require attaching the sewer hose to 2 places rather than 1, but it sure would be faster AND a complete draining instead of leaving some greywater in the tank to get nasty.