I recently had a similar problem when selling a property. Our septic tank was across a road and in the garden of a neighbour. My neighbour did not use it and had his own tank. It had been there for 70 years but we had no paperwork.It cost us £1500 for a Deed of Easement to be registered with the...
I have a septic tank that half my roofs rainwater runs into as does my neighbours.It does not cause us any problems.
We also have an exemption certificate that allows us to discharge 4 cubic metres per day from the tank onto the surrounding land........no problems for us and it saves us £500+ a...