I've bought a new button push flush valve and the bloke at b&q said to get a close coupling set too. After quite a long time trying to get the old fittings off, as it was rusted, i put the new part in through the hole in the tank and the coupling was too small at 1.5 inch. I went back to shop and that is the only size they do even though I bought the flush valve their too and asked advice. My question is , do I need a coupling kit ? does the rubber ring go around the outside of the big screw bit ? Thanks for any help !
Can you post pics of your cistern/ valve. There are various fixing methods and two sizes of valve. Don't know what your set up is.