But we cant sell the house with an illegal septic tank...

https://www.tallents.co.uk/septic-tank-regulations/

€œIf youre selling a house with a septic tank that discharges into a watercourse, then the sale of the property will trigger the requirement to upgrade or replace the tank before the deadline of 1 January 2020 and before the sale completes.€�"

SINGS:
Theres a hole in my Bucket, dear Lisa, dear Lisa...

[GEORGE]
On Sunday, August 25, 2019 at 11:48:07 AM UTC+1, wrote:
On Sunday, 25 August 2019 11:03:12 UTC+1, George Miles wrote:
any advice and experience please?

It may be easier simply to move house.

Owain