Underground soil pipe solvent weld

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gh483

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Hi, not sure if this is should be in the plumbing or building forum. I want to install a new ground floor toilet which involves teeing into the existing soil stack below ground level. I have already cut a 4 metre long trench through the floor slab and dug out enough material to install the pipe and pea gravel infill etc.

I am looking at the 110 mm, terracotta-coloured PVC pipe and fittings for sale in the DIY sheds, but one thing that confuses me is that it is all push fit. This seems risky for something which will be inaccessible after the trenches are covered over with fresh concrete and any leaks or perished seals would be impossible to repair. I would have expected solvent weld would be recommended in this situation, but no-one sells it? What is the answer?
 
I see, any advice on how to ensure that the joints will never fail or need to be accessed?
 
Come to think of it the push fit for mitigation of expansion and settlement make a lot of sense in a long run outside where the pipe is just buried in an earth trench, but shouldn't be as much of an issue underneath the building slab where the consequences of a leak are also that much higher. Is it still normal practice to use push fit instead of solvent weld actually underneath the slab?
 
If it's fitted right using the correct pipe and fittings, there won't be a problem. If you are a diyer, have you the correct skills ? I am a plumber but use a skilled drainage man for any underground work.
 
gh483 said:
Come to think of it the push fit for mitigation of expansion and settlement make a lot of sense in a long run outside where the pipe is just buried in an earth trench, but shouldn't be as much of an issue underneath the building slab where the consequences of a leak are also that much higher. Is it still normal practice to use push fit instead of solvent weld actually underneath the slab?
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I worked for Severn Trent Water for over 40 years and have seen many miles of pushfit drainage pipe laid in all sorts of materials and sizes go in, some pushed into place with the back of a JCB bucket. If water companies are happy with 1000s of miles pushfit couplings I think you can be. The only time we tend to use continuosly welded pipe is on water supply pipes, a bit like the yellow gas pipes you see being installed but bigger and in blue.
 
Virtually every material used for gravity underground drainage relies on rubber gaskets to make an airtight seal. From 100mm pipework upwards, even the large box culvert sections use a flexible seal, so you'll be quite safe with a 110mm plastic pipe. Should it ever start leaking, then the accepted method of repair now is to line the pipe from a suitable point, by inverting a large 'sock' and curing by a preferred method, to form a structural liner within the host pipe. Laid correctly, the chances of it leaking are slim, and of ever needing to dig it up again are virtually Nil.

Fusion and Butt welding is only ever used on pressurised pipework, i.e. pumping mains.
 
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