If the height of the outfall of the Python, is not that much lower than the substrate in the tank, this may be the problem. Much has to do with head pressure.
If your tank is in a room with the substrate 4 feet off the floor, and the outfall and faucet of the Python is attached to is 3 ft off the floor, this is very little head pressure.
If however your tank is on the 1st floor(ground floor), and the outfall of the Python is in a basement (10 ft lower) you may find suction would probably be overkill.
I find using a regular siphon with a hose run out a window to my garden and lawn, works much more effectively.
After trying this method, I built permanent PVC lines to the garden, with a stand pipe opening attached to a window. Instead of Pythoning it down the drain, the old water gets a 2nd use, and helps fertilize the garden besides