Yes and no. If you use a 15 amp receptacle, you can do it. That has no t-shaped slot. If you want to have an outlet that you can plug a plug a NEMA 5-20P plug as well as a NEMA5-15P into, make them both 20 amps with 12 gauge wire. You can put a NEMA-5-20 receptacle (parallel slots and no T) on a 20 amp circuit. I suspect that is the plug (parallel blades) that is on your sump pump. So with that 15 amp receptacle, you can do as you propose.
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