As Tom points out it is the water in the hose. You can reduce the volume by replacing the hose with a thinner diameter hose.
A one inch ID hose will hold 1 cup every 18 inches.
A .75 inch ID hose will hold 1 cup every 32 inches.
A .5 inch ID hose will hold 1 cup every 73 inches.
A .25 inch ID hose will hold 1 cup every 294 inches.
This of course reduces the max capacity of your bilge pump. The default install on my boat was a single hose with a .75 or 1 inch diameter (don't remember). I am replacing this with the system recommended by Don Casey: Installing a Bilge Pump by Don Casey
"The ideal bilge pump arrangement is a small (400 gph) automatic bilge pump mounted in the sump to dispense with rain and shaft-gland leakage, combined with a high capacity pump (3,500 gph) mounted higher to deal with more serious ingress.
Stepping the discharge hose from the small pump down to 1/2-inch minimizes the backflow from the hose when the pump cycles, maintaining a dryer bilge... the high-capacity pump sits high and dry, extending its life indefinitely."