The revenge of the leaking toilet

This is why I don't undertake plumbing repairs.
I got so fed up of the phantom flush on the toilet next to my office and the outrageous price the plumber wants to charge ($350 for a basic fix that involves $20 of Home Depot parts or what he would really like to do is to take out my nice one piece toilet that matches the tiles and replace it with a cheaper two-piece in white that will look hideously out of place for the amazingly low price of $750) that I downloaded the instructions from ehow.com and prepared to tackle it myself. Reading through my eye was caught by the following tip:
Check the bowl-fill tube if you're still getting "phantom" flushing. If the bowl-fill tube is below the water level in the tank it can result in a siphoning action that sounds a lot like a leaky flapper. Adjust or trim the tube so that it's above water level - this will provide an air gap to break the siphon.
Aha I thought, that's the cause. So I pulled the hose out a little and replaced the cistern lid and went off to get changed to go to dinner. All dressed and ready to go, I visited the bathroom before venturing out in the February cold, flushed the loo and watched as water poured out of the cistern. Stupidly, I wrenched off the cistern lid, allowing the hose its freedom to spray cold water all over me, and the bathroom floor. Darn, darn, darn.
I think I need another fix.