I run my water out of the door as well to save water when draining the tank. As another user posted about priming the hose, it works. To note on this as well, if your python has a white lever used to stop and start the water flow, you can close that, fill the hose up from that to the syphon part, submerge the syphon part upside down under water, then open the valve.
Once you get the hang of it, its real simple..kinda tricky to get started tho til you get down how to prime it.