Andrew wrote:

snip

Why can't I connect it to the waste stack ?. - i.e. well above the 'high
tide mark' ?

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Andrew (change P to K in s.ydata to reply)

ROTFL!

You may have had a genteel upbringing and never participated in a 'light the
fart' experiment in your teens.

Waste gasses both directly from humans and indirectly from decaying waste
material such as in drains contain methane which is inflammable.

You migth get a blowback in the toilets etc

Bob