"Peter Crosland" wrote in message
...
Also, would I be right in thinking that detergents can have a negative
effect on a septic tank?

So, water from gutters, washing machine, bath/shower/sink should *not*
be run into it.

Instead gutters should run into a ditch;

They should run into a soakaway not a watercourse

Only for a new installation. Many old buildings have a ditch to collect
roof rainwater and lead it to the nearest stream.