On Tue, 4 Dec 2007 08:57:48 -0800 (PST), The Real Doctor
wrote:

According to a vey useful book about septic tanks which I bought at
CAT last year, the bacteria are practically indestructible.

You don't just need to "have bacteria in" a septic tank, you need to
have a population that's largely of the right sort, and you need to have
them working for you. If you affect the oxygen availability in there
then you might not kill them off, but you'll stop them working in favour
of the anerobes (the hydrogen sulphide makers).