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I am planning on fitting an en suite shower and baisin and want to run the waste from these to the WC waste / soil stack which runs down the opposite corner of the room (house is old with many modifications over the years and there are a large number of hidden voids above ceilings).
I can run the waste under the floor (parallel to the joists) but the existing WC waste bends and runs horizintally just below the joists so I do not have a vertical section clear of joins where I can fit a clamp on boss to take the waste pipe.

I do have access (just) to the horizontal section of the soil pipe where it runs above the ceiling below, can I fit a boss such that my waste pipe enters the soil pipe vertically from above?

I guess I'll need anti syphon traps on the baisin and shower wastes. Should I run these two wastes separately?

If it is what I think you mean, yes you can do that. There are only a couple of considerations you must consider.

Imagine looking down inside the horizontal WC pipe, you can only cut a connection in it above the horizontal, ie, from the 9 'O' clock position through 12 to the 3 'O' clock.

If the connection to the pipe is near the toilet end, and the fall on the WC pipe is minimal, there is a small chance some waste water will flow the wrong way and end up in the toilet bowl.

Unless the new pipe runs are long, there is no need to use special traps.

Always run basin and shower wastes separately otherwise when the basin plug is pulled, water will come up into the shower tray.

[quote="plumbbob"]If it is what I think you mean, yes you can do that. There are only a couple of considerations you must consider.

Imagine looking down inside the horizontal WC pipe, you can only cut a connection in it above the horizontal, ie, from the 9 'O' clock position through 12 to the 3 'O' clock.

If the connection to the pipe is near the toilet end, and the fall on the WC pipe is minimal, there is a small chance some waste water will flow the wrong way and end up in the toilet bowl.

Unless the new pipe runs are long, there is no need to use special traps.

Always run basin and shower wastes separately otherwise when the basin plug is pulled, water will come up into the shower tray.[/quote]

Thanks, pipe entry would be at the top of the pipe (12 O'clock) so should be OK.

Hi, just read your reply (horizontal soil running under floor), you made reference to not running w/b into shower waste pipe.Does that only apply when a shower is involved in the run? Many thanks.