Plumbing - law of unintended consequences

[AndyPandy]

In our kitchen we have a waste outlet that is fed into from two directions.

Firstly the sink via a u-bend
Secondly the washing m/c and dishwasher via a sloping down pipe, open at one end (or was) for the m/c.

Nothing unusual about that setup.


The sink pipework develops fatbergs and every 5 years or so I strip it out and remove them all. Usual symptom is a pong from the sink indicating a dismantle is required.
This time the pong seemed to find its way back to the washing m/c and washed clothes had an aroma to them. Even after said fatberg was removed there was a whiff.

Long story short, I fitted a U-Bend to the open end and fed the machine into that. This seems to have fixed any smells drifting back but now the sink gurgles, presumably because the new airlock stops equalisation of pressure and forces air the 'wrong way' round the sink U-Bend.

It may well be that if we'd have waited long enough the air would have become fresher, but I didn't. Apart from taking out the new U-Bend, any suggestions as to how to stop the gurgling? I know it's a First World problem, and we can live with it, but if there are any simple suggestions, I'm happy to try them. Small vent hole in the machine downpipe?

[staffordian]

Any possibility of not using the washing machine pipe, blocking it off and instead routing the outlet into the sink U bend using something like this?

https://www.screwfix.com/p/floplast-sin ... 40mm/12794

I think you can get them with two branches so the dishwasher pipe could also be dispensed with, assuming the relative position of the appliances allow.

[jfgw]

I'm not sure how your washing-machine was plumbed in but there should be a trap (U bend). In almost all cases, the waste is fed either into a standpipe, https://www.screwfix.com/p/mcalpine-sta ... 40mm/94360 , or into a spigot on the sink trap, https://www.screwfix.com/p/mcalpine-app ... 40mm/81714 . If you use a spigot on the sink trap, make sure the waste hose from the washing-machine loops up and back down before it attaches to the spigot otherwise you will get sink water in the washing-machine.

If you get gurgling, either there is a partial blockage or there is a problem with the design of your pipework. You might be able to cure the gurgling with an anti-syphon trap, https://www.screwfix.com/p/mcalpine-ant ... 40mm/20226 . I much prefer tubular traps like this one, https://www.screwfix.com/p/mcalpine-swi ... 40mm/50408 which looks like an anti-syphon trap even though the description doesn't say that it is.

Julian F. G. W.

[AndyPandy]

Couple of good ideas there to follow up. Thank you.

A couple of additional questions have arisen as a consequence of the answers.

The washing m/c has an outlet that just hooks over a open vertical outlet pipe There's some stiffened plastic (to keep the curved shape). Is this OK to then plumb directly into an airtight connector?

The washing m/c feeds into a pipe that runs behind the dishwasher and then a bit more to reach the drain. The sink is immediately on the other side of this. If I was to convert the sink u-bend to take another input would that be too far for the m/c (The waste pipe would be about doubled in length). I don't know how much welly the water pumps have *.


* Thinking laterally, an alternative would be for the d/w to feed into the sink (should just about reach) and the washing m/c could then go into the vacant d/w connector (should just about reach).

I will experiment.

[bionichamster]

If you have space to fit one then an air valve on the pipe coming from the washing machine might be the answer. Splce a 'T' joint into the pipe with a vertical section topped with a one-way valve. This will let air into the pipe and equalise the pressure with outside rather than have the air gurgle in from the sink via the Ubend.

The one-way nature should prevent any liquid escaping the other way but I'd fit a vertical section anyway to be sure. I've done this myself when I've had a u-bends that are connected to long lengths of pipe, the further a big lug of water travels down the pipe the lower the pressure gets, fitting a valve somewhere along the length or even at the top end near the U-bend made sure it didn't then suck all the water from the u-bend.

This is the sort of thing, although there are cheaper ones :https://www.screwfix.com/p/floplast-af32w-air-admittance-valve/42968?_requestid=218664

This site explains their use in soil pipes, but same goes for waste: https://www.drainagepipe.co.uk/soil-and ... nce-valve/

BH

[bungeejumper]

The washing m/c has an outlet that just hooks over a open vertical outlet pipe There's some stiffened plastic (to keep the curved shape). Is this OK to then plumb directly into an airtight connector?

Doesn't sound like a great idea to me. The flexible hose (that presumably sits into an open vertical stand pipe?) relies on the air gap to stop any back-pressure from other (blocked up) parts of the system. Dishwasher waste in the washing machine wouldn't be too good.

Maybe not quite relevant, but I have a similar sink/dishwasher set-up in my kitchen (except that my sink is a double with two separate waste traps), and every three or four months I run the d/w at maximum temp, half load, with a cup full of Flash floor cleaner instead of d/w detergent. It seems to have stopped the fatbergs which used to plague us. And it doesn't half smell clean afterwards!

BJ

[jfgw]

The washing m/c has an outlet that just hooks over a open vertical outlet pipe There's some stiffened plastic (to keep the curved shape). Is this OK to then plumb directly into an airtight connector?

If the machine is connected to a spigot on a sink trap, it is vented via the sink waste/overflow. This is by far the most common method.

You can get self-cutting connectors which bolt onto a waste pipe but these connect downstream of the trap. This is not one of the methods shown in any washing-machine instructions I have seen and, while it would probably work fine, I, personally, would use one of the methods I outlined previously.

If I was to convert the sink u-bend to take another input would that be too far for the m/c (The waste pipe would be about doubled in length). I don't know how much welly the water pumps have *.

Discharge hose extensions are readily available and I have never known them to cause a problem with the machine. The most likely problem I can think of that you may encounter is if you purchase a new machine from one of the chains and expect them to install it for you. Their installers may refuse.

Julian F. G. W.