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I am trying to install bathroom waste pipes (for shower and sink). I am struggling over getting solvent weld joints in the waste pipe that I am happy with.

The summary of what I have learned from watching numerous Youtube videos about doing this is:

  1. It's easy
  2. You need to ensure there are no ragged edges on the end of the pipe after cutting
  3. Dry fit your parts and mark with a pencil line to ensure you get the right alignment when you come to use the solvent weld
  4. Put SW on both the pipe and fitting
  5. Push the pipe right into the fitting up to the stop
  6. Do a quarter turn as you are putting them together.

I am unfortunately not finding it so easy: I basically end up with massive snots inside the joint, far worse than burring if I wasn't deburring the pipe. I worry about these causing blockages and/or the joints leaking because I've not got a good enough weld.

I think the problem stems from the fittings being incredibly tight: if I put them together dry, I struggle to get them fully in, and then struggle to get them out again. It's easier with the solvent weld on - I guess it's acting a bit like a lubricant - but I still can't get them fully in, and the SW squeezes out of the joint as snots.

I've tried doing a few practice joints, and I found that just putting SW on the pipe, and it's much better in terms of the snots; but I still don't seem to be able to get the pipe right up to the stop in the fitting. I also worry about going against the advice of needing it on both parts.

I am using 40mm Aquaflow solvent weld pipe and fittings, bought at Toolstation.

Can anybody suggest what I'm doing wrong, and/or whether an alternative brand of pipe/fitting would work better?

Thanks.

Edit: a particularly snotty joint photo:

enter image description here

A bit of the snot pulled out of the joint:

enter image description here

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  • Pictures of a couple joints you're concerned about would probably help immensely in determining if you're doing it right or not, but it sounds like you're doing the exact right thing to me.
    – FreeMan
    Commented Oct 4, 2022 at 12:03
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    Thanks @FreeMan, I will post some pics when I get home
    – Andy
    Commented Oct 4, 2022 at 12:26
  • @FreeMan please see the photo I uploaded.
    – Andy
    Commented Oct 4, 2022 at 17:42
  • In the US, black plastic pipe is ABS, while white is PVC. Are you certain you're using the correct glue for that pipe?
    – FreeMan
    Commented Oct 4, 2022 at 17:57
  • @FreeMan it's pvcu according to Toolstation's site toolstation.com/solvent-weld-waste-pipe-3m/p87411, but the glue is suitable for pvcu and abs toolstation.com/pvc-pipe-solvent-cement/p70177
    – Andy
    Commented Oct 4, 2022 at 18:06

3 Answers 3

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The pipe joints are tapered. They only fit right when softened by solvent. You should not be attempting to get them fully in when dry-fitting, it should not even be possible to do so. The dry-fit is mostly about getting the angles correct.

Process wise, I use cleaner, primer and cement, on both parts, per the instructions. The former two products are considered optional by some people - the primer may or may not be required by the LAHJ. I consider using all three as cheap insurance against potential issues I'd rather not have.

You can deburr both the inside and outside of the end of the pipe, which may reduced your "snot" issues slightly. But the snot is not a particularly big deal. You may also be getting overly enthusiastic on cement in the socket - the pipe only goes to the stop at the bottom, and your glue application should be similarly placed - anything past that point will not contribute to the joint.

One additional possibility (should not be the case unless you are using old cement) is that the cement (but not, IME, primer or cleaner) can thicken with age until it's not actually any good to use.

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  • ...and if somone is going to link that stupid YT vid claiming primer makes joins worse, that does so by assembling joints incorrectly for a male bovine byproduct "test" - spare me. I've already debunked it once.
    – Ecnerwal
    Commented Oct 4, 2022 at 12:44
  • "the pipe only goes to the stop at the bottom" I don't understand what you mean by this, could you explain please?
    – Andy
    Commented Oct 4, 2022 at 13:24
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    @Andy Most pipe connections will have a ridge(stop) a few inches in. Can usually see it on the outside where the connection(elbows) expands to go over the pipe.
    – crip659
    Commented Oct 4, 2022 at 13:32
  • @crip659 yeah, I can see that, I don't understand what is meant by "at the bottom" - the stop is all the way round, no?
    – Andy
    Commented Oct 4, 2022 at 18:09
  • It's at the bottom (or end, if bottom confuses you) of the socket, all the way around. It is the place that the pipe "bottoms out" when fully inserted.
    – Ecnerwal
    Commented Oct 4, 2022 at 19:44
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The process you are using is correct. Always put the solvent on both the pipe and fitting. You may be using too much solvent resulting in a lot of "snot". Try using less solvent on the fitting, ( still applying to both the fitting and pipe) The snot is really not a big issue. I often wipe away excess solvent after 20 seconds or so. It's makes for lots of messy rags but works very well. You probably have concerns from inexperience, but what you are doing is correct.

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  • "The snot is really not a big issue" the thing that I'm struggling with it the idea that these big snots aren't important, but far smaller burrs on the pipe are.
    – Andy
    Commented Oct 4, 2022 at 12:27
  • Snots are smooth, burrs are sharp. Things slide over snots, and get caught on burrs.
    – Ecnerwal
    Commented Oct 4, 2022 at 12:32
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Thanks very much to the people who took the time to answer.

Despite your assurances that I was doing it right, I remained a bit uncertain that I was - in particular, the fact that I couldn't push the fittings right together, which is the way that several of the UK-based DIY channels show it being done on YouTube (e.g. Plumberparts, The DIY Guy etc).

I decided to give another brand of pipe a try - I was in B&Q, and tried the fit of Floplast:

  • it was just that little bit easier to put together dry
  • the Floplast-branded ABS glue seems a bit thinner so easier to spread rather than sitting in a bit thick lump so...
  • it doesn't squeeze out quite as much
  • and it felt like what I was expecting - ultimately, I have to live with my choices :D

So, that's what I've gone with. Thanks again.

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