Replcing Flapper valve with a shires syphon 7 ltr?

Okay my main problem is the fact I do not have the plastic tube coming from the bottom of my cistern. Instead it sits on the back of the toilet base. There is no pipe apart from the overflow on one side and the water feed on the other. There are two wing nuts (I think that is what they are called) situated on either side of the back of the toilet base which the cistern sits on. I assume these release the cistern subject to the other two pipes and I hope the syphon. Any ideas? Many thanks in anticipation.