is the water level of the tank lower or higher than the output level of the python? The reason I ask is that most if not all gravel vacs are just a syphon - no mechanical or other type of propulsion - the only real requirement is that the output of the syphon be below the water level of the tank and the lower it is, the more suction the syphon creates.
If your sink-driven suction is insufficient or you are "pulling uphill" the best bet might be to use a bucket on the floor and syphon it out for just the vac part of maintenance.