Over time, laundry detergent collects and solidifies in the bottom of the measuring cup.  It wastes detergent, and makes your measurement inaccurate over time.  

This Laundry Detergent Cup Drain Back Funnel keeps from developing a detergent sludge in bottom of measuring cap/cup.

This works specifically with the All 1.44 Gallon container.  There are many different thread configurations, so your mileage may vary.