Badly routed waste water pipe, slow draining sink

[stuckinstandby]

Hello, I'm looking for some advice on how to tackle this... We have a slow draining sink in our utility room. When the washing machine pumps out water, it comes up into the sink before slowly draining away. I think some of the water may drain back to the washing machine. This has been a problem since we moved in 2 years ago.

We've established that this is due to the alignment of the waste water pipe. I've been under the floor boards and found that the pipe was sagging. I added a couple of supports which has reduced the sag but due to other pipework it wasn't possible to get it straight (there's a T off the cold water to a garden tap which obstructs the waste pipe).

The waste pipe runs 4.5m towards the front of the house (perpendicular to the flooring joists) and then turns 90 degrees. 2.5m from the turn is the kitchen sink which has no issues. 2.5m further is the stack. Where the pipe turns, it has to go upwards to get over the foundation wall and then down towards the stack.

So I seem to have a few issues here but I think the main one is the upward turn. To resolve this it looks like I'll need to cut out a brick from the foundation wall.

Does this sound like the right way to go with this?

I've attached a couple of photos.



Thanks

 

[JCplumb]

What size is that pipe, it looks 40mm? A 4.5m run is too long for 40mm. Might just get away with 50mm but the waste pipe size rules are:
32mm - 1.7m; 40mm - 3.0m; 50mm - 4.0m.
That's without it sagging and then going uphill.
Considering that the total run length is a lot more, you're really faced with using 3'' or even 4'' soil.
You can't be notching joists for that diameter of pipe so you're left with taking it under the joists then out. You only need about 1cm drop per 1m, so the total drop on the 4.5m run would be fine if it was 5-6cm.
Would it be possible to do it this way? If so then you know what you need to do

 

[stuckinstandby]

Yeah, it's 40mm. The bricks are 7cm so that plus the mortar and wood should give me enough for the drop. I can't access beyond the bend so can't be sure what the drop is there.

If I was to change the pipe for a larger one how would that work with joining to the existing 40mm pipes? like the u-bend under the sink and the pipe after the 90 degree turn? I'm guessing the entire run would have to be larger for it to be of real benefit?

I found another photo showing how it was before I added a couple of supports. This is looking towards the bend but from closer to the sink.

 

[stuckinstandby]

EDIT: Double post

 

[JCplumb]

You can't drop back down to 40mm, you'll need to run 3"(82mm) all the way to the soil.
There are connections you can buy that will do it, but their intended purpose is for a smaller dia pipe to feed into a larger one, not the other way around.
You're begging for blockages if you do it that way.
If you're going with 3'' then you'll need an 82mm boss to join into the soil pipe, you'll need a 40mm boss(for an 82mm pipe) where you're joining the sink waste to the 3''soil pipe and an 82mm end cap.
3'' fittings are hard to come by in the sheds, when I've needed them before I went to drainage online - convenient as they have everything you'd need, but they're not cheap.
If you want to be able to pick the fittings up off the shelf in one of the big sheds then go for 4"(110mm).
You could always choose to have pumped waste but it will need an electrical connection and will probably cost a fair bit more in the long run with maintenance/repairs etc.
Have a look at the sanispeed if you're thinking of going down the pumped route, we have a macerator/pump expert on the forums if you need advice about that. @rpm

 

[stuckinstandby]

Thanks JC. I can't access the pipework after the bend and on to the stack without ripping out a newly fitted kitchen. If only I'd realised how badly installed this was, I'd have had it done before the kitchen.

It sounds like the best thing to do first of all, is remove a brick in the wall (actually two walls back to back) to lower the bend and then adjust the supports to try to correct the sagging.

Hopefully this will be enough to make the sink usable and I can revisit the pipework when we eventually replace the kitchen.

I did read something saying that two 45 degree bends are better than one 90 degree. Would that be worth trying if lowering the bend doesn't improve things significantly?

 

[Martin63]

The macerator idea is a good one, also have a look at Saniflo. I've serviced a few of these and they are not difficult to maintain. It's a utility room so the electrical connection should be easy enough and you could even plug an extra WC into it if you so desire..

 

[rpm]

Pumped waste doesn`t like a rise unless it is at the start of the pipe run, it will work but you will shorten the life span of the pump motor. At the moment you only need a water pump however you can fit a macerator and blank off the 4" inlet if you think you may want to add the toilet at a later date.
45 elbows x 2 are better than 1 90 for the water to flow.

 

[stuckinstandby]

So, an update... I've not had much time lately to try to sort this out and the job itself has taken longer than expected. Removing the bricks in the walls was difficult in such a tight space and those bricks were laid short end facing out. But I have now literally made a break-through.

With the bricks removed I was able to drop the pipe a few inches at the turn. It's definitely made a difference to the sink draining but not quite as much as hoped.

The pipe itself has warped from being in the poor position for so long. Even with a few supports and props it's not possible to get the pipe straight without stressing the pipe too much (in my opinion).

The other issue is the T off the cold water to the garden tap which obstructs the drainage pipe about 1 metre from the sink. Having to go under this, results in a drop of 5cm in that metre, over the next 2.5 metres the drop is to around 6cm and the last metre is near horizontal. Due to the warping of the pipe, I found if I lower it in some positions it raises it at the bend.

So the professional would no doubt just replace the pipe, but before I get on to that, is it likely that the warped pipe will recover to a more normal angle if held in a better position for a period of time? Can anything be done to help/speed this?

I think removing the obstructing pipe to the garage tap will also help by allowing a more gradual drop over the run (and I need to do this regardless). I have a few questions on doing this - I'll probably post another thread since it's a specific problem.

Any guidance appreciated.

 

[Stigster]

The pipe can be warmed to bend it but I've only ever done that when I needed to make the slightest of bends or a "kick" in the pipe. Trying to straighten it over that length, all whilst not burning it (using a blowlamp set low and keep it moving) or kinking the pipe would be a nightmare in my opinion.

I'd replace the pipe.

 

[stuckinstandby]

Thanks, Stigster. Looks like I'll have to replace it. I'll probably also try to change the 90 degree bend for 2 x 45 degree bends while I'm at it. First up will be dealing with the obstructing garage tap.

 

[Ric2013]

If it was sagging below horizontal it will be partially blocked and so it will not drain properly. It also appears to be leaking at that first 90 bend. Should be clipped every half meter. I see this sort of thing a lot, sadly.

As others have said, textbook plumbing would require no more than 3m for 40mm. Above this, either increase pipe size, or add ventilation pipe (see Approved Document J online page 10 for what I'm on about). I think the lengths are more about traps getting sucked out than about flow rates. Obviously a bigger pipe will be better, and I would always prefer to see 50mm on a sink plus washing machine even on a short run.

Use two 45s or a swept 90, not a knuckle 90 wherever you possibly can..

If I wanted a simple solution (i.e. if doing it properly is too much work), I'd upgrade the pipe size if possible, make sure there was a steady fall on the pipe (18mm/m is the official minimum, but, as others have said, do the best you can as any fall is better than nothing). If the pipe size ends up being greater, I'd fit traps with air admittance valves with the knowledge that they will probably make a gurgling noise in use (but it's a utility room).

I still think 40mm would be sufficient flow based on the fact that my old kitchen waste had a washing machine on a 5m run of 40mm pipe and it worked. But, unlike yours, it had a fall (even though it was generally a fairly poor installation).

 

[stuckinstandby]

Thanks Ric2013. I think it's just glue that you can see in the photo, rather than a leak. I'm not able to easily increase pipe size without ripping out a new kitchen and floor (the length after the bend is inaccessible otherwise).

I was hoping to make a start on replacing the pipe during recent holidays but things never worked out so I decided to get a professional in for a quote.

They've suggested fitting an air vent under the sink as a first step and see if that improves things sufficiently.

 

[oz-plumber]

The air vent will do stuff all.
The waste pipe will be full of solidified waste from where it is sagging.
From the pics, thats a lot of gunk sitting in that pipe.

Just replace the horizontal section that you can easily access with the correct fall and clip the pipe so it can't sag.
If you do replace the pipe, you may find it then necessary to install an AAV

 

[stuckinstandby]

Thanks Oz. I think the idea was that he would want to fit the AAV regardless so might as well do it first and see how it helps, before deciding to do the rest.

Worth saying that I have repositioned the pipe since the original photos, by removing bricks, changing existing clips and adding other supports... and a bit of wood.

I've taken some new photos. In these, the sink is to the right and the right-angle turn towards the left. The lagged pipe running across is the obstructing pipe leading to an external tap. There's a bit of wood 3/4 of the way along preventing the pipe bending further upwards.



If you're thinking that the pipe will be clogged due to previous sagging, is it worth pouring some acid down to see if it helps? I did that when the pipe was in it's initial position and didn't notice much difference. Maybe now the pipe is better positioned it would help, albeit temporarily?