If you are sure the blockage is definately in the pipe one method is to remove the hose and run a garden hose through it but often you cannot get enough pressure to clear it. This is going to sound CRAZY but i have done it lots of times and it works every time :- remove the hose and go out in the garden away from everything and swing the hose in a circle above your head as fast as you can holding just one end, like a lassoo. The centrifugal force generated in the hose forces the blockage to fly out of the end, theres just the embarassment factor to overcome if neighbours are watching! Cheers
Kenjo
June 2012