That little spongy, doughnutty thing between your toilet cistern and toilet can sometimes get a little squashe, frail and maybe permit a small dribble to escape...yes, you know the problem with small dribbles, don't you?
Instead of going to B&Q and buying a big stupid rubber doughnut that doesn't give or deform and so doesn't work, you need this.
Refresh your sanitary ware seal, stem the little leaks, all for substantially less than a Tena....you see what I did there.