I have a leak coming from the back of my toilet, from what i believe to be known as the flush pipe? I have looked all over the internet and not seen an attachment like the offending part anywhere? See image. It is a close coupled toilet, but with this connection feeding the water from the cistern upon flushing.
Quite a substantial amount of water comes out on every flush, from where the red arrow is pointing.
Before I undo it to see what is causing the leak, I wondered if anyone has seen this before, or should i be warey that parts dont exist for this anymore (im guessing it will be a new rubber washer/flange job). Or what I am expected to find under there. I dont want to take it off and not be able to put it back in a fixed state.
Also any safety tips (not flooding my house!) plus gerenal advice/tips would be appreciated.
p.s. As you probably have guessed im an amateur plumber!