Firstly you have a new type flushing toilet. It has been designed to flush with the minimal amount of water 6 Lt Full flush and 3 Lt short flush. If you introduce a a brick or bag into the cistern you will find your self flushing the toilet twice as often with little effect.. DO NOT DO IT !!!!!!!
Now for the flush When you removed the cistern top you pulled out the two plastic rods they are " T " shaped if you look at them end on... These rods locate into the button flush on the lid they also are different lengths one large for full flush and the other short for short flush. ensure you have the rods in the right holes. Then before replacing the cistern lid remove the buttons from the holder and ensure you place the lid correctly over the two rods. You will now have the lid on with the two rods poking through the button holes. Try the short flush rod first see if it does what it should ! Then follow it with the full flush rod push. If that works fine carefully fit the flush buttons over the rods and again test before inserting the lid securing screw . if it all works fine secure lid replace screw and do not play around with it again. These cisterns will not work well if you start playing around with their inners.
Pat
December 2008