Light came on toilet cassett so went to open outside toilet door and tried to pull cassett out to empty but cassett just would not slide out. Thought cassett might be too full so mopped out (5 to 10 litre) fluid from hole through toilet seat (not a present job) but cassett till would not slide. Anyone can help please I am new to this I have only empty the cassett once before and it slided out no problem Thanks in advance