Siphoning system

Hi all,
now I have problem on best system to siphon my 40g tank every 15 days during water
I understand that best is using an air pipe and discharging water into a can. The
little diameter of pipe will result enoght time to work. 
But my little gravel (2-3 mmillimeters) tends to clog the pipe.... and the suction
power is very little... 
May somebody explain better how to do?
Thks & rgds
Ciao  Ezio                _ _
______________________,,,_o o_,,,_______________________
  FERRO Ezio                             Torino - Italia  
              Quando il gioco si f duro,
               il duro che inizia a giocare.