Least worst way to plumb in new sink waste

[PythonCrazy]

Morning All,
Just after some advice as I have been asked to plumb in a sink and washing machine waste for a new kitchenette. The other side of the stud wall shown is the bathroom, with the toilet attached to the soil pipe bottom right and a small basin attached to the 32mm waste. The wall is tiled closely around both pipes. Both disappear below the stud wall, into the ground at this point l and I'm not able to reach down to the base of the 32mm waste where I presume it connects to the soil pipe. Soil pipe terminates at a manhole 10-12 meters away and is entirely underground from this photo onwards.

Question is this, which is the least worst way of connecting, given that digging up the concrete floor of the extension isn't an option!

A - Cut the 32mm as far down as I can reach and connect a 40mm pipe with a 40mm AAV to plumb all 3 lines into. They are never all likely to be in use at the same time. Or
B - Insert a solvent weld boss on the back of the soil pipe elbow and find some way of securing it given access all the way round is v limited. I'm concerned that a boss in this position might snag toilet roll etc and leak to a blockage.

What are your thoughts on these options? and are there any other ways of doing this?

 

[Ben-gee]

Do not put a sink and a washing machine into the 32mm!

What is the arrangement in the bathroom? Could you take a 40mm waste into there and boss it into the 110mm behind the toilet?
Are you aware there are pan connectors with 40mm compression bosses - this might get you out of trouble here..?

Obviously you still need traps for sink and washing machine in the kitchenette- probably a sink waste trap with spigot for appliance will be easiest.

 

[PythonCrazy]

Do not put a sink and a washing machine into the 32mm!

What is the arrangement in the bathroom? Could you take a 40mm waste into there and boss it into the 110mm behind the toilet?
Are you aware there are pan connectors with 40mm compression bosses - this might get you out of trouble here..?

Obviously you still need traps for sink and washing machine in the kitchenette- probably a sink waste trap with spigot for appliance will be easiest.

No, I didn't know you could get pan connectors with 40mm bosses on. Thank you! I'll have a look. I have the kit to drill through the tile so should be possible to put a 40mm through to the left of the soil pipe. Does the boss need to be vertical? Or could I angle 45 to fit it in under the cistern?

 

[Ben-gee]

Best on top of the soil pipe, worst on side (ok, worst underneath!) anything inbetween is in between!
So 45 is probably ok but higher up if you can.

Is there nowhere else you can get the waste to? This will be suboptimal- but it should work.

 

[Timmy D]

What’s people thoughts on this...

The visible face of the 110mm elbow, at around the 45 degree angle, looks flat enough that if you drilled a hole, it would take a standard boss. You could heat it up with the blowtorch and mould it to adjust the boss shape and get a good fit.

Or it might take a mechanical boss.

Or drill the hole and get a 110 elbow with built in 40mm branch and cut the branch and enough area around it to make your own boss....

Just thinking out aloud.

 

[BN9Pete]

What’s people thoughts on this...

The visible face of the 110mm elbow, at around the 45 degree angle, looks flat enough that if you drilled a hole, it would take a standard boss. You could heat it up with the blowtorch and mould it to adjust the boss shape and get a good fit.

Or it might take a mechanical boss.

Or drill the hole and get a 110 elbow with built in 40mm branch and cut the branch and enough area around it to make your own boss....

Just thinking out aloud.

I would stick to thinking out aloud and gas 😧 😂

 

[Ben-gee]

I’m just thinking of ‘stuff’ in the pipe hitting that bend and catching on the boss…

 

[Ric2013]

Hmm. I've seen OLD sinks run in 32mm and they had 1.25" wastes.

Actually, I've seen (abroad) a 1" waste pipe (not 1.25") serving a washbasin (and shared with a bidet), with the washing machine outlet hooked over the basin itself, and the washbasin didn't back up, so I'm not sure that 32mm is actually insufficient flow, though the pipe running full-bore may induce siphoning out of the trap.

If the washing machine tees into the pipe rather than using an upstand, it may be that the worst case is slow draining or backfill into the sink rather than disaster, and, particularly if you add a secondary vent or an AAV to prevent siphoning out at during full bore operation, it might be a workaround that would not cause major issues. I would, however, want to reduce the diameter BEFORE the washing machine connects to help prevent the chance of slow flow running into the washing machine (though if that happens, I'd suspect there is a blockage anyway).

I'd be very hesistant about cutting into that bend with a saddle boss, as, if it ever goes wrong (perhaps due to abuse by the occupant), you've left the goal wide open to claims that it's your fault for fabricating a 'bespoke' fitting. Whatever you decide, you need to consider the possible things that could go wrong and how big a deal they are likely to be before choosing the way ahead.

 

[BN9Pete]

I wouldn’t even think about cutting a boss into a soil bend, I would walk away from a job if someone wanted me to do that.
Think I’m far to professional but more of a worrier 😆

 

[Ric2013]

Best on top of the soil pipe, worst on side (ok, worst underneath!) anything inbetween is in between!
So 45 is probably ok but higher up if you can.

Is there nowhere else you can get the waste to? This will be suboptimal- but it should work.

Best on top? I was reading about hospital systems that essentially have a horizontal stack and in those systems it is actually preferred to come into the side rather than into the top of the horizontal stack. Apparently coming into the side promotes linear flow and prevents whatever is in the water hitting the bottom of the pipe and sticking/splashing/noise problems. So I'd intuitively say it would make sense to come in sideways to a pan boss, but that's not based on actual experience (have come in sideways to a 50mm branch with various kitchen 40mm wastes, and that worked very well, but it's not quite the same thing).

Or is it a different scenario in your opinion, given that the water and solids are leaving the WC in a turbulent fashion compared with the horizontal stack water movement that has had time to straighten and smoothen its motion between one sliproad and another?

 

[Ben-gee]

I’d say that if something dropped into the soil from the top, right close to the pan, it will be easily moved on by the next full flush!

Coming in too low on the side leaves you far more likely to get paper/solids catching on the bossed in junction and therefore potentially building up and blocking the small diameter pathway you are trying to use for the sink etc.

I did say that this whole scenario is sub-optimal, I personally would find another route to waste even if this involved digging up the floor that the OP said they didn’t want to do.🙂

 

[PythonCrazy]

So, I solved this with a pan connector with boss attachment per Ben-Gee's original suggestion. I was able to get the boss positioned vertically and drilled through the tiles above the soil pipe so the waste is hidden from view by the cistern and I have a happy customer. It also means that if anything catches and causes a blockage, it's likely to be accessible without breaking open the wall again.