Lol, where but MFK would people be advising others how to create this:
...when they started with this:
OP, some of those fancy designer faucets don't have easily removable, standard-threaded aerators and make the installation of a Python a royal PITA. And I have had some unpleasant failures in the past when trying to use those universal rubber collars; sometimes it seems as though "universal" means that they literally don't fit anything.
Before you start "improving" the crap out of your bathrooom or kitchen faucets, consider using the hose bibs in your laundry room that supply water to your washing machine. You can put a valve-controlled Y on both the hot and cold, and then leave the washer connected to one side of the Y and just use the other for your Python. You'll want a 2-into-1 adaptor to allow mixing the temperature when re-filling the tank.
You can just suck-start the siphon to empty the tank, allowing it to drain into a bathtub...or, you can add a shut-off valve to the end that goes into the tank. Drop that into the tank with the valve open, fill the hose up from the hose bibs, shut the valve, move the hose to the drain, open that valve and let the siphon empty your tank to the desired level, then shut the valve again and return the hose end to the hose bibs to refill the tank.
I don't recall if the Python mechanism lets you attach a hose to the bottom of the thing? If it does, it gets even easier; attach the Python to the hose bibs in the laundry room, run one hose to your tank, a second hose to your drain, and then perform the entire water change without doing anything other than opening and closing the appropriate valves to drain, fill, etc.