Does anyone know the location of an online resource I can use to get my head
around how the internals of a toilet flush should work?

It's just that mine is becoming reluctant to flush, despite the float valve
aparently working fine (the cistern fills). One thing which might cause it is
that the washer on the actuator attached to the handle is lifting (I think it
should stay in place sealing the top of the lower chamber). Would this cause
reluctant flushing?

**** description, I know, trouble is I know so little about what the bits are
called that I'm struggling to describe it.