The vacuuming strength of the Python is dependent on the water pressure coming out of the faucet, as well as on any height differential between the tank and the faucet.
Even on tanks that sit at floor level (and hooked up to a faucet at standard height on the same level of my house), I have plenty of suction to vacuum gravel.
I turn off my faucet and just let the siphon pressure do the work, it's strong enough to pick up some of the gravel and get it to the top of the tube before I can shake it back down.