drain problem

[Biguns]

Got a job to do for a friend, dentists surgery
Sink unit takes for ever to drain. Pipe from bottle straight down through unit and floor under joists. Then horizontal for 600mm, then up again for 50mm
(in other words a huge 'u' bend under the floor) Then horizontal again for 13 metres under the surgery, waiting room and toilet outside through concrete into a manhole " a nightmare"

Thinking of fitting one of these:-

http://www.saniflo.co.uk/sanivite.aspx

Never had any experience with them. Any advice/ comments would be appretiated.

 

[Biguns]

Forget it just read instructions. all horizontal pipe runs must have 1;100 fall