We had what might seem a simple drainage issue, it was not, it required a delicate balance of heights between pits so as not to allow light showers to enter the top pit or back flow from the bottom pit but only allow entry to the top pit where heavy rain may enter our flat. This was dependant on other drains in the area and their load under stress.
Jetty plumbing was very professional in ensuring that this critical height (about 10ml) of the top drain was perfectly placed. They came back twice at their cost after different rain events to check that this system worked perfectly and it did.
Jetty plumbing are fantastic."