"The Natural Philosopher" wrote in message
...
On 27/07/2020 21:24, NY wrote:
a mini sewage works - at great cost, and making a constant loud hum from
the motor that stirs the contents.

A mini sewage works, at about £8000 and almost completely noiseless but
impossible to fit under a patio

The only person I know who has a mini sewage works is someone that I
sometimes deliver the local parish magazine to, and the hum of his sewage
works is audible from about 100 yards away - he's got it positioned as far
as possible from his house to minimise the noise that he can hear from the
house or garden. It's about the same noise at 100 yards as standing right
next to a noisy fridge. Maybe his sewage works is an early model and more
noisy that modern ones.