Adding the Higginsons Syringe to your enema set up, allows you to overcome liquid flow obstructions through occasional gentle pumping.
This helps greatly in avoiding cramps and achieving a thorough colon cleanse. 
It is particularly useful when your bag/can is not elevated much and so the gravitational pressure on the water is low.
This item has built-in one-way valves to ensure the water does not get sucked back up the tube. It comes with its own nozzle, so your existing nozzle simply plugs into it.

Approximate dimensions:
Overall length inc nozzle - 67cm
Length ex nozzle - 60cm
Diameter of pump - 46mm
Length of pump - 80mm