I know the post above is kind of past it's sell by date now, nevertheless this may help someone, my Father in-law who used to be a builder / carpenter / come plumber, he passed on to me a tip for clearing blocked toilets, he swore by plunging them using nothing more than an old fashioned string type mop. I've used this method myself and so far touch wood, its never failed, & is substantially cheaper than chemicals or mechanical methods.
