Partlially blocked kitchen sink drain?

At my mum's house the kitchen has a full-size steel sink with a half-bowl drainer next to it. When the plug is pulled out on the larger sink water flows away, but slowly, and some comes up into the half-bowl drainer.
Underneath there's lots of 2" (or so) diameter plastic pipe in various lengths fastened together with screw-rings on some pieces threading onto threads on other bits, with rubber washers, and in one or two cases fitments that seem to use a compression washer and fit against an unthreaded plain pipe. These pieces connect the half-bowl to the main sink's outflow, above the trap, then the flow from the trap goes into plastic pipe that looks to me as if it's solvent welded to adjacent bits.
This latter welded pipe starts at the extreme back righthand side of the undersink cupboard. I cannot get any tool or my arm or anything else further to the right). The pipe has a downward section (3" perhaps) then a right-angle bend and flows from right to left by about 12", then another right-angle bend towards the rear of the under-sink area and then it goes out through the house wall. I think it then meets a cast-iron downpipe, about 2 feet above a small access hatch in that 4" downpipe.
I've taken apart and cleaned all the screwed-together bits of plastic pipe; they were a bit gungy but nowhere near blocked. On the other hand the fixed plastic pipe that all the screwed-stuff is connected to feels to to me as if it may very well be gunged-up, though I took as much gunge out as I could with my finger.
I bought some "one-shot" drain cleaner at B&Q; it's clearly concentrated sulphuric acid. I've read some reviews of it on Amazon; some people say it's great but a significant minority say their use of it has burned through their plastic pipe, or maybe through washers/seals leaving them with a really horrible acidic mess to clear up, and I'm not keen to add that to the problem. The instructions for the stuff say one pours 125ml of acid down the sink, waits 5 minutes, then adds some water... but it seems to me that all that that would do is replace the water in the trap by acid, maybe diluting it a bit in the process. There's no blockage in the trap or before it. Then more water would flush some or all of the possibly diluted acid into the lower reaches of the drain, where some of it might linger long enough to make a difference.
Maybe I'd be better to try to tip it directly into the solvent-welded section of plastic pipe, rather than the clear section above the trap?
Maybe I'd be better not to use it all? Can one get bendy brushes (like bottle brushes?) which can be pushed down a 2" pipe to extract gunge?
I guess I can open the small hatch in the downpipe, but ecen if there's signs of any blockage there I can't see that I've much chance of doing anything useful because the kitchen drains enter that pipe 2' higher up.
Any advice?
--
Jeremy C B Nicoll - my opinions are my own.

Email sent to my from-address will be deleted. Instead, please reply
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On 08/01/2014 18:06, Jeremy Nicoll - news posts wrote:

I'd try this type of thing before messing with strong acids. Any plumbers merchant if you're in a hurry.

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

http://groceries.asda.com/asda-webstore/landing/home.shtml #!product/910000041727 The plunger, not the beans .......

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Wed, 08 Jan 2014 18:51:04 +0000, stuart noble wrote:

+1
I'd much rather use a manual/mechanical method of unblocking. You do really need to use it with a flow of water to wash the broken up bits of gunge down through the restricted bit of pipe, not so vital if working against the normal flow (as one should).
I guess many people reach for the chemical solution as they don't understand the problem and/or are squeamish about a bit of smelly, yuky gunge. That's why you can get rubber gloves...
--
Cheers
Dave.
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On 08/01/2014 18:51, stuart noble wrote:

You can get thin flexible steel strip on a handle, but provided that the water will drain away but slowly I'd be inclined to use a caustic based drain cleaner. It has always worked for me.

Also given the nature of the sort of cold fatty gunge that accumulates in kitchen sinks I think strong caustic sold in a gel formulation as proprietory drain cleaner is far more likely to work and less dangerous.
Concentrated sulphuric acid generates a lot of heat when added to water (and vice versa is *extremely* dangerous).
Both are wear eye protection and rubber gloves but the caustic is a little bit less likely to blow back or melt the plastic due to overheating on contact with the water in the trap.
--
Regards,
Martin Brown
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Caustic certainly boils when dissolving, and is hot enough to melt a plastic cup (don't ask! :-) )
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On 10/01/2014 11:30, stuart noble wrote:

Yes but you can get a gel formulation drain cleaner where the major exothermic reaction has already occurred (and for anyone not used to handling nasty chemicals I would always recommend that approach).
It also has the advantage of sinking to the bottom of the trap. I wouldn't worry too much about the soap swelling either the warmth and extreme caustic environment should keep the stuff in solution long enough to flush it with good hot water.
DO NOT look down is to see what is going on even with eye protection.
You have to be more careful if there is no path through at all since then you can end up with noxious chemicals stuck in the trap. (and definitely don't change from acid to alkali part way through!)
--
Regards,
Martin Brown
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

The blockage isn't in the trap, or above it - those pipes are all fine. The problem is lower down... As the sink still drains fairly well I fear that any caustic or acid solution will not hang around long enough in the part-blocked area to do any good.
--
Jeremy C B Nicoll - my opinions are my own.

Email sent to my from-address will be deleted. Instead, please reply
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

That can be a problem. You could have a small hole through a large fat blockage, most of which would be untouched by chemical treatment.
http://www.zen31010.zen.co.uk/images/yuck.jpg
Tim
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On 11/01/2014 07:33, Tim+ wrote:

If your pour hot fat down a drain you deserve all you get
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Though for us we suffered for previous owners behaviour.
We suffered from the drain blocking (underground, from the kitchen), due to fat from the previous owners. which I think was partly blocking the drain, which then caught other stuff until it blocked entirely.
Had to have a couple of goes with the drain cleaner attachment for the pressure washer before it was clear. We had some great big lumps of fat come down the pipe.
--
Chris French


Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Wednesday, January 8, 2014 6:06:53 PM UTC, Jeremy Nicoll - news posts wrote:

The first port of call is to throw caustic soda down the drainpipe, and wait. 99pstores currently have it. If that fails you could take pipework apart to clear it. Yes there are other options. http://wiki.diyfaq.org.uk/index.php?title=Unblock_a_Drain
NT
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On 08/01/2014 18:06, Jeremy Nicoll - news posts wrote:
<snip>

<snip>
Well I have read the description on Amazon but is it *really* concentrated sulphuric acid? In my opinion that is certainly the wrong thing to be putting down any drain, especially if you have cast iron downstream. It won't attack plastic pipe but it may cause degraded rubber seals to disintegrate further. It is also likely to have a go at cement joints if you have ceramic drainpipe downstream.
As others have said, mechanical cleaning is usually the best bet, although caustic soda is also quite effective on fatty deposits. IMHO the "fancy" cleaners which TV ads show working in transparent pipework are all snake oil.
Hydrochloric acid aka brick acid is effective for lime deposits and not quite so unpleasant as sulphuric (but don't get it in your eyes). It will attack some metals.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On 08/01/2014 22:04, newshound wrote:

It certainly is. About 91% IIRC, PH less than 1 !!.
Most plumbers merchants sell One Shot, as do B&Q, Homebase, Plumb Center. I've used it a number of times on blocked toilets etc.
How the hell do Amazon convince a carrier to deliver it?
> In my opinion that is certainly the wrong

I don't think it's there long enough to do that. It will however completely strip the chrome plating of of a waste fitting & badly stain GRP baths.
--
Dave - The Medway Handyman www.medwayhandyman.co.uk

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On 08/01/2014 18:06, Jeremy Nicoll - news posts wrote:

If you haven't used One Shot before, please be aware it is SERIOUSLY nasty stuff. Don't even think about using it without gloves & eye protection.
Whatever you do, don't just pour it into the sink, it will permanently discolour stainless steel & take the chrome off the waste fitting.
Poured into the plastic pipe it should be fine, if flushed withing the time specified. It comes in a plastic bottle after all :-)
--
Dave - The Medway Handyman www.medwayhandyman.co.uk

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Wednesday, January 8, 2014 10:54:45 PM UTC, The Medway Handyman wrote:

+1.

Caustic doesnt affect chrome or GRP, it comes dry making it safer to handle, and its much faster on grease, which is the usual blocker.
NT
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On 08/01/2014 23:45, snipped-for-privacy@care2.com wrote:

In kitchens it's usually oil/fat. Problem is that caustic usually increases the volume of the blockage by converting it to soap, and that can give you another problem.
In bathrooms it's invariably hair, and acid is better for that. That said, I've never known a waste pipe that I couldn't clear with a "snake", or a garden hose, or a metal coat hanger, or something else I've got lying around. I think Dave is right about people (even men!) being slightly squeamish these days. Obviously never had kids :-)
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Thursday, January 9, 2014 9:26:37 AM UTC, stuart noble wrote:

Caustic normally works in bathrooms too IMLE.
Soap is very soluble in boiling water btw, and helps to clear the fat.
NT
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

BTW?! The sodium salts of animal fats are often larger than the original fat, hence the build up of sewer soap in big cities. It has to be dug out with a spade despite being (in theory) water soluble
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Friday, January 10, 2014 10:01:54 AM UTC, stuart noble wrote:

Well, they'd need a hell of a big kettle to melt it! :)
NT
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.