Drilling Soil Stack

On Tue, 22 Nov 2005 00:13:04 -0000 someone who may be "Rob Convery" wrote this:-

I wouldn't want to do that. Connections should not be made to the stack within 200mm of the centre point of a lavatory connection. This is to avoid the possibility of the lavatory discharge blocking or obstructing smaller waste pipes.

Instead make the connection at least 200mm above or below the lavatory connection, using a suitable boss. Whether it is above or below depends on your plumbing. The hole can be made with a suitable hole cutter (into a plastic stack).

There are patent fittings to avoid this, but I suspect it would mean dismantling the stack to insert one, which you may not want to do.

Thanks for that, sounds like the easiest thing is just to join the waste with the basin in the bathroom which I am pull the water feeds from. The amount of waste will be minimal as its only for washing hands so should be fine

That's just about it. Cut out the hole with a padsaw or something, and cut the ragged edge off. You could go into the soil stack using a strap boss.

If the connection is made opposite the lavatory one, 200mm below, that seems to be in the perfect position for being blocked! That said it doesn't seem to happen IME.

There is/was a sort of drilled rubber bung type affair for doing this. Haven't seen them for a few years (but then again I haven't been looking for them.)

sponix

On Tue, 22 Nov 2005 08:57:48 -0000 someone who may be "Rob Convery" wrote this:-

You may need anti-siphonage traps on both basins if you do this. Single stack plumbing works well when someone who knows what they are doing is designing it. However, the various recommendations are there for a reason.

On Tue, 22 Nov 2005 09:18:29 +0000 someone who may be Chris Bacon wrote this:-

After falling for over 100mm the lavatory discharge is presumably going vertically and thus unlikely to block a smaller branch. If the smaller pipe is connected closer than 200mm then I imagine there is still a horizontal component to its motion and so it may block the smaller branch.

Having thought about it a bit more I suspect that the 200mm above recommendation is to avoid siphoning water out of the trap in the smaller waste.

That demonstrates that those who cam up with the recommendation were right:-)