The answer to 'why is my sump pump slow draining' is that there are several common causes, including a blocked or clogged sump pump intake, a malfunctioning sump pump, or a problem with the drainage system. Slow draining can be caused by debris, mineral buildup, or a pump that is too small for the size of the sump pit.
If the sump pump is slow to drain, it may be due to a clogged intake screen or a problem with the impeller. Mineral buildup or debris can restrict the flow of water through the pump, causing it to work harder and drain more slowly. In some cases, the sump pump itself may be failing and need to be replaced.