We've recently moved into a new flat and recently the push flush button on the toilet keeps sticking in. The cistern is hidden behind the bathroom shelf and we have to take it off every time to fix it. I've never seen this type of flush mechanism before but as far as I can see the button forces air down a tube which pushes a rubber bung up which moves the flush up to flush the toilet. When the button is depressed the air comes back in the flush falls back down on top of the bung and (supposedly) the air pushes the button back out. It seems like the air is not coming back in and that the pressure when the button is pushed is actually forcing the bung out of it's socket which could be the reason why the air can't get back in to push the button back out...phew! To remedy it we have to remove the rubber air bung from the pipe to let air back in and the button returns to normal. This used to happen once a week, now it's every day and the bathroom shelf is permanently off so we can reach the cistern. It looks like a cheap and nasty job to be honest. Any tips on what I can do or where I can replace this bung? (apologies if it's not called that but I can't find a name or picture for it anywhere)