in cistern there should be a long threaded plastic screw, turn this clockwise and more water will enter cistern. keep turning until there is enough to get rid of all waste.
if this doesn't work you will be better off getting a plumber to replace syphon. prices for these vary from £3.50 to about £10.
a plumber will charge around £20 to £30 for labour, pay no more, it is a simple job.
tommy
November 2009