Hi @jakewiffen8,
Thank you for your question and welcome to the Bunnings Workshop community, it is fantastic to have you with us.
You're looking at your flush pipe, which transfers water from the cistern to the toilet bowl. The leak is likely due to a degraded seal on one end of the pipe. Assuming your pipe is 50mm in diameter, you can replace the seal to the cistern with this 50mm Flush Pipe Ring and the seal to the bowl with this 50mm Pan Cone.
You'll have to start by draining your cistern and toilet. It's worth keeping some towels handy at this stage as some spilled water is certainly possible.
Turn off the supply to your cistern at the stopcock that can be seen in your second photo. Once the supply is off, flush the toilet to remove the water from the cistern. You can then use a towel or sponge to remove any remaining water in the cistern.
You can then force flush the toilet with a plunger or by pouring a bucket of water into the bowl. This will create pressure that starts the siphon action that occurs during regular flushing.
Once drained, undo the nut that connects your flush pipe to your cistern. You will then be able to remove the pipe and the pan cone. You can then replace the seal and the pan cone, reconnect everything and test to ensure there are no further leaks.
If replacing these parts does not fix the issue, I'd suggest contacting a plumber for their assistance.
Let me know if you have any further questions.
Jacob
