new shower waste (double trap) & toilet waste run to septic tank

30 Dec 2003
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United Kingdom
Hi All,

Struggling to find a plumber, so tackling this myself. This is a new install (single storey) so will need waste piping all way to the exiting septic tank. Would like to run a few things by you..

Would a 'stub stack' the way forward with this? With boss pipe for the x2 40mm wastes then a branch for the toilet? (with 1:40 slopes on all)

The toilet will be nearer to the tank than the shower but to save on complex piping and a cleaner install I'm thinking it is better to site the stack directly behind the toilet?
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Stub stack with an air admittance valve on the top would be the preferred option I'd think. Stack can go in the corner is need be, 110mm pipe can come across to the WC as required. Connect shower using a boss, note if also fitting a basin, AAV will need to be above the spillover height of the basin.
thanks Hugh, yes good point - would also need to install a sink as well.

I also read that by regulation sub stacks are not permitted outside but it is common practice that they are
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Biggest problem with them externally is the AAV freezing in the winter months. Use an external AAV and I cant see there would be a problem. Alternatively, as ground floor, connect WC directly to drain and provide a gulley for the wastes. I assume existing system/tank is vented elsewhere?

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