Hi Lucy,
These Roco "Flushers" are notoriously bad for leaking. I've just been trying to fix a leak myself and try as I might it just keeps leaking. Was checking online to see possible suggestions and came upon this.
Hopefully this is not too late a response, but in answer to your question, you need to remove the two "push buttons" (Depress one and lift the other up) to reveal a plastic screw. Unscrewing this eases the plastic sheath off and then allows you to remove the lid.
Hope this helps.
Arno
Arno
December 2007