Toilet siphons are most often used in the UK and Europe. These differ from the flapper type assemblies used most often in the United States in that they use a siphoning action to draw water out of the toilet and into the bowl to carry away sewage. When you press the handle on these types of toilets, it pulls a plunger inside the siphon, which starts the siphoning action. Because the siphon is such an integral part of the flushing assembly, you should replace it as soon as it starts malfunctioning.
Turn off the water to the cistern at the water supply valve. This is usually located beneath the toilet. Rotate the knob clockwise to turn off.
Flush the toilet to empty the water in the cistern. Remove any remaining water with a cup or other container. Wipe up any remaining water with a sponge and towels.
Remove the float ball. This is the ball assembly that raises and lowers with the water level. It's not necessary to remove this as part of the toilet siphon replacement, but getting it out of the way will make things easier. Unscrew the float ball from the valve assembly. Unhook the handle assembly from the hook on the siphon.
Place more towels underneath the toilet.
Use the pliers to unscrew the nuts holding the siphon in place at the bottom of the cistern. Water will probably drip out, but that's what the towels are for. Reach into the cistern and remove the siphon.
Wrap the screw plugs at the bottom of the new siphon with plumber's tape. Insert the new siphon into the tank so that the screw threads poke out through the bottom of the tank. Ensure that the rubber bung protectors sit flush on the bottom of the cistern or you may have leaks. Secure the siphon in place with the screws from the bottom.
Hook the end of the handle lever to the link on the siphon. Replace the ball float by screwing it back into the fill valve.
Restore the water supply and allow the tank to fill.
Flush the toilet and check for proper operation. Tighten the siphon fittings if necessary.
Come prepared with plenty of towels. Plumbing projects always seem to require more towels than you think.
The above steps are just a guideline. Always follow the specific instructions for your siphon model.