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Install wall hung toilet & in-wall cistern

I have just moved into a new - second hand house. The upstairs en-suite has had a new toilet fitted recently before I bought it (very badly tho') I have bought a new 'wall hung toilet / in-wall cistern / frame & flush box & would like someone who knows how to install it correctly to help me please. The waste pipe may also need adjustment but can be fully accessed from behind the wall. The last installation / set-up is quite frankly poor. Can someone who knows what they are doing please help me. Thank-you in advance.