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I bought a countertop dishwasher. Home Depot did not have adapters to connect my faucet to the included quick-connect adapter. I have also heard that the hoses in pull-out faucets are not meant to withstand full line pressure as done by this blog post.

So I want to install a tee on the hot water line and connect that to the dishwasher. Here's what I have to work with:

  • Hot water pipe: 3/8" compression (male)
  • Dishwasher input: thread OD 26.33mm (1.037"), 4 threads per 7.28mm (0.287", 14 TPI). I think this is 3/4" MIP/NPS.
  • A hose that connects to dishwasher and terminates with a nut (14.48mm/0.57" ID) and washer. This matches a male end on the quick-connect adapter which is 15.4mm (.607") OD, 7 threads in 10.16mm (0.4"). I am not sure whether this is M16x1.5mm, 5/8"-18TPI, or something else.

I would like to re-use the hose but don't know what it terminates in. So without that, here's what I've got using hardware store parts:

wall: 3/8" Compression male
3/8" compression tee
3/8" compression supply line
3/8" compression to 3/4" MIP (NPT) adapter
3/4" FIP (NPT) coupling
dishwasher input: 3/4" MIP

wall==>     >══╦══>   >==================<      <==>                   >==<        <====dishwasher
3/8 comp       v        3/8" comp hose     3/8 comp to 3/4 MIP   3/4 FIP coupling      3/4" MIP
          3/8 comp tee
               v
          to sink hose

This is a lot of parts and brass adds up quick. How can I reduce part count? I tried looking for e.g. a 3/8" comp to 3/4" FIP hose, but even McMaster-Carr only has 3/8" comp to 1/2" FIP. Do they make 3/8" comp to 3/4" FIP bushings? This guy with an identical-looking dishwasher spent $90, which I do not want to do.

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    Have you tried at a plumbing store/shop? Stores like where you went, usually only stock stuff that moves fast and is common for most things.
    – crip659
    Mar 29 at 0:12
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    Do you want to use the quick-connect? Or, in any case, what's the other end / half /part of the quick-connect got on it for threading? Many similar quick-connects have an option to GHT (Garden-Hose Threads) for clothes washing machines (and some portable dishwashers) which can easily be gotten from a boiler drain valve (that you'd Tee off your supply line.) Indeed, I'd wonder if your dishwasher input is actually GHT, not NPS. That would mean a mis-measurement of pitch, but that can happen.
    – Ecnerwal
    Mar 29 at 0:46
  • You could add another line coming through the escrusction that the faucet is mounted and add an additional hose bib there, That should be fairly inexpensive,
    – Gil
    Mar 29 at 0:48
  • @Ecnerwal unfortunately, I only got the plastic end of the quick connect (it was a used dishwasher). I know that GHT is common for inputs on the rolling "portable" dishwashers, but I think the threads are too fine. Mar 29 at 4:31

2 Answers 2

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The faucets for old clawfoot tubs also have a 3/4" MIP connection, and they make braided flex supply lines for 'em. Use the 1/2" FIP x 3/4" FIP flex line instead of the 3/8" flex you were going to use. Adapt from the 3/8" stop valve (or a 3/8" comp. tee, if necessary) directly to 1/2" MIP with a little special adapter made for exactly that scenario, to accept the tub flex, which will attach directly to your portable dishwasher . These are likely plumbing shop items, as opposed to "big box" (and don't be surprised if they are cheaper at the plumbing shop...

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  • Total cost prolly less than $35, and fewer fittings Mar 29 at 2:58
  • Thanks! I'll find a plumbing store and report back. Mar 29 at 4:32
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    An even better option (IMO) would be to change out your supply valve (angle-stop valve) with a dual-outlet valve that has a 3/8" compression outlet (for your faucet) and a 1/2" MIP outlet (for the dishwasher; they make them, I have one under my kitchen sink). This would further reduce the number of adapters/fittings, but would require more work, money, and shutting off the water. Mar 29 at 16:17
  • Nice, I'd do it if dual-outlet valves were cheaper than the tee and adapter, or if I owned the building. Swapping out a part instead of just adding means I have to store the single valve for when I leave this apartment. Have yet to visit plumbing store, hopefully they have a long enough hose. Mar 29 at 17:53
  • No luck on the hose. I'm accepting this answer, since it gives one way to reduce part count, and adding what I actually did for future confused dishwasher buyers. Cost under $35 as you predicted so it all worked out. Mar 30 at 2:17
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The plumbing store didn't have a long enough 1/2" to 3/4" FIP line and I was getting antsy. So I bought something close to my original parts list for a total of $30.70. For future readers, here is what I got:

  • 3/8" compression tee, 1 female 2 male. $10.39, #4225030
  • 6' supply line, 3/8" compression. $10.64, #DW872
  • 3/8" compression to 1/2" MIP connector. $4.34, #102631
  • 1/2" FIP to 3/4" FIP coupling. $5.33, no part number.

I installed the tee right after the hot water shutoff valve and connected the sink hose and dishwasher hose to it:

installed 3/8" compression tee

I connected the 3/4" to 1/2" adapter to the dishwasher, the 1/2" to 3/8" comp adapter to that, and then the hose to that. It is very easy to crossthread a plastic piece when you're attaching a metal piece to it. I used PTFE tape and wrenched it pretty tight, but it still drips a couple drops during the dishwasher cycle, hence the tray underneath.

hose to adapters to dishwasher

And finally, I just pointed the original drain line into the sink. The PVC under the sink doesn't have an easy place to tee in the hose, and this is a $25 dishwasher, so I didn't feel like putting more time into the project.

ziptied hose draining into sink

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    I'm glad it worked out, if you ever have to do it again, there is a tailpiece for the sink drainpipes commonly called a "branch wye" or "dishwasher wye" that is made to accommodate a hose connection to the under-sink drain system. It would make it a cleaner installation. Mar 30 at 3:48
  • I know, there's just not an obvious vertical section of pipe between sink drain and P trap to swap for a wye. I'd have to find a very short wye or drop all the drainpipes. Mar 30 at 7:16

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