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Replacement parts for General Electric GSD720P-35BA | AppliancePartsPros.com

The big question is did it used to or is this a new install.
Note the drain hose has to be looped up higher than where it enters the house plumbing.

The way these pumps work is that the drain solenoid (left hand side of pump behind the kick plate) is actuated for a couple seconds, the solenoid plunger is pulled down. This moves the wash/drain flapper valve in the pump to the drain position. The water pressure then holds the flapper in the drain position until the unit is empty and then the springs on the solenoid lever return the flapper to the wash position.

Could be that the flapper is stuck in the drain position.

Also many of the flappers have a black seal/bumper in the center of the flapper perhaps this is missing and water is being pumped out as it washes.
Click on the picture of the pump in the parts and you will see this in the middle view of the pump.