We have just successfully done this, with the help of an earlier thread. Question from rpm is valid, we had removed our cistern so been able to take a good look at all its bits. Replaced parts (genuine Geberit from PlumbinBits), & put them in exactly as the old ones had come off. Push white pipe in as far as it goes, the fat black 'washer' in - the writing side facing up towards the cistern & the clip pushed in after it, tallest edge facing up towards the cistern, it then sits in a groove there, located just inside the lip of the fixed 'down' part. Makes no difference that there is a small gap in the clip, only to aid getting it off I presume. All carefully done identically to the picture you have here. We have NO leaks.
We don't have a brace on the flush pipe because the elbow is too close. Discovered some weird thing with the installation of the cistern, which I won't explain, but it allowed far too much 'play' when you put even the lightest pressure against the lower half of it. Felt that may be compromising the flush seal when the toilet is pushed back, so we ensured the cistern was hanging properly straight down, & I reached in to hold it from being pushed backwards as best I could while the toilet was pushed into place.
We're on our 2nd toilet now, same leak problem. Hopefully we'll have the same result. 3rd one has the faintest sign of 'dribbling' starting in the pan, but confident we can sort that if it gets worse. Suffice to say we will eventually dump these Geberits should they start leaking again.
No idea why I joined this site with my husband's name, I'm finding all the solutions to problems & doing half the fitting!
