"Dave Liquorice" wrote:

On Wed, 5 Dec 2007 00:19:40 GMT, brian mitchell wrote:

Rainwater is a no, no. The volumes of even a small shower on a decent
sized roof will flush a septic tank through far to quickly...

What is the ill effect of that?

Well apart from the fact the muck doesn't stay in the tank long enough to
acted on by the bacteria effectievly the sludge gets washed into the
soakaway blocking it up...

Thanks, also to Charlie Pridham.
My system (also on a Welsh 'mountain') had nearly all the roof runoff
plus grey- and blackwater running through it when I arrived. I'm
gradually diverting the rainwater but expect to leave the greywater as
is, though there's no biological soaps or other heavy-duty cleansers
used.

I have to say, though, that the system --which is easy to inspect--
seems to look and function exactly the same as it always has, without
needing emptying and with a clear soakaway chamber. Perhaps being on
extremely well-draining land makes the difference.