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I am replacing the rusted out plumbing (drain, p trap, tee, trap adapters, 45 degree elbow) under my kitchen sink with ABS, but I notice that some fittings offer a choice of hub or spigot connections.

There are a couple of places (particularly an elbow and adapter connection) where I can arrange the connections so the water will flow from a hub into a spigot, or a spigot into a hub. But I don't know if one way is better than the other.

I tried searching "abs spigot hub flow direction", but the only relevant result (among many, many irrelevant Home Depot links) was for PVC, which indicated flow from the spigot to bell (hub) would encounter a square edge that had a marginal effect on hydraulics. But looking at the ABS connections, it seems the opposite - the square edge is encountered when going from hub to spigot.

But I am more concerned with drain pipes and which orientation will be less likely to trap waste from the garbage disposal and other small bits that typically goes down the drain of a kitchen sink.

hub-spigot diagram

Is there any preferred or conventional way of arranging ABS spigot/hub connections with respect to the flow of waste water?

isherwood
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fuzzydrawrings
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  • no difference with drain; matters with hvac/dryer and similar vents which use friction/crimp/screw fittings with an *exterior* sealant (tape/mastic) – P2000 Jul 19 '21 at 21:47

2 Answers2

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It makes no difference with cement-welded pipe. If you install a wye or tee or other splitter you inherently have one of each anyway. Also keep in mind that enough cement and dissolved plastic tends to push out at that area that the interior shape of the part (sloped vs. square) becomes somewhat moot.

I suspect that you're actually referring to "street" fittings--those without a hub on one end. Those exist mostly for ease of fitment in tight areas and a few other special cases. It's not about flow direction.

I'm not a plumber, but I've done a lot of plumbing and watched many good plumbers work on new homes when I was a builder. I don't recall anyone ever making the distinction you have in your post, nor have I heard the term "spigot" applied thusly. It's just not a concern. Good luck with your project.

isherwood
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  • Thanks! Regarding the "spigot" designation, I was trying to use the terminology I'd seen in H.D. product descriptions. But they also have "street" in the description but I didn't make the connection between it and lack of a hub (although I was wondering what it meant). So in addition to answering my question you cleared up some confusion I was having about the term "street". – fuzzydrawrings Jul 20 '21 at 00:23
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In theory the "hub fitting" is always better than the "spigot fitting", regardless of the flow direction because the former gets attached to the exterior of the pipe, while the latter gets attached to the interior of the pipe and therefore it introduces a flow restriction. The picture from OP is inaccurate because in both situation it shows a hub fitting, just reversing the flow direction. To show the difference between the two fittings it should be modified as below.

enter image description here

Below is a picture from Home Depot of two different fittings used to join two ABS pipes of same diameter, the left one is denoted as "hub-spigot" and the right one is the standard "hub-hub". enter image description here

MarcoD
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  • Thanks. Seems a "[spigot fitting](https://www.pvcfittingsonline.com/resource-center/pvc-end-types-descriptions-and-explanations/#:~:text=A%20spigot%20fits%20inside%20a,are%20often%20called%20street%20fittings.)" is essentially the same as a reducer bushing in some cases. The downstream pipe in your drawing should probably be of a smaller diameter. #til – isherwood Jan 31 '23 at 13:58
  • Hi isherwood, that would be the logic use of a "spigot fitting" in my view as well. However, the Home Depot site shows a "hub-spigot" fitting to join two ABS pipes of same diameter, in addition to the standard "hub-hub". The only case I can think of in which I would choose the former is if there was no room to increase the diameter of the pipe I needed to extend. I added a pic showing the two fittings to my answer. Note also that the terminology is a bit confusing, the "spigot fitting" described in your link, with the same size around as a regular pipe, is called street fitting by Home Depot – MarcoD Jan 31 '23 at 22:52