Should I tie a new dishwasher drain hose to an unused 1.5" drain stub or to the kitchen sink drain?

[Golden_Days_Pete]

I’m installing a new dishwasher, and spent several hours researching, but can't find out a few key things. I discovered this site a week ago, and I've joined as a premium member with this as my first post. The condo builder 20 years ago left a 24”w space under a counter by the sink for future dishwashers. The rear wall has a water inlet metal stub, electric outlet and a 1.5” PVC drain stub. The stubs are about 8” above the floor, and stick out 2-3”. I bought in July and I’m pretty sure a dishwasher was never put here. The drain stub was covered with duct tape, which I removed to view. I don’t have a garbage disposal and never plan to have one. It seems like my two drainage options are either:

A) Connect to the sink drain. I don’t like this due to the drawbacks of: I’d have to drill a hole through the cabinet, it would expose my sink cabinet to another leak point, and I’d need to find a branch tailpiece that fits with my existing double-bowl set-up (see photo below) … and install it. It would also mean a longer hose length, but does it matter whether a hose is 7’ versus 10”?

B) Connect to the drain stub. I have concrete walls in and out. In the wall, the 1.5” pipe right angles straight down at least five inches after the bend. I poked a flexible inlet hose in, and several inches of it continued down past the turn without hitting anything. My questions about approach B are:

1) I don’t know what the drain stub connects to or how far down it connects. Does that matter, and if yes, what’s the possible issue? I’ve read a lot about having a high loop. If I put a high loop behind the dishwasher, would that be enough to avoid issues with using the unused stub? For example, does the dishwasher drain flow need a p-trap somewhere along the way?

2) The owner’s manual says: “Make sure to connect drain hose to waste tee or disposer inlet above drain trap in house plumbing and 20" (508 mm) minimum above the floor.” Do you think that only applies if I’m connecting to my existing sink plumbing … or would it also apply to connecting to the unused drain stub? If it applies to the drain stub, is it workable to install a drain tee onto the stub?

The manual also says: “It is recommended that the drain hose either be looped up and securely fastened to the underside of the counter or be connected to an air gap. Make sure to use an air gap if the drain hose is connected to house plumbing lower than 20" (508 mm) above subfloor or floor.” Do you think the last sentence is only referring to a situation in which I connect to the sink plumbing? Or does it also apply to the unused drain stub? The stub is only 8” above the floor, not 20”.

So far I haven’t been able to find an adaptor or connector to transition from a dishwasher 3/4” drain hose to the 1.5” stub out, which is about 1.8”w on the outside. Does such a product exist and what is it usually called? The first photo below shows the stub outs. The second photo shows the nearby sink plumbing.

I’d prefer to use the stub out drain, but I definitely don’t want to install an air gap. So if an air grap would be essential for using the unused stub out, I think I’d sooner settle for having the drawbacks of connecting to the sink drain. I'd really appreciate any and all advice. Pete

 

[MicEd69]

One would "ass-u-&-me" that if the builder went to the trouble of plumbing a stub out for a dishwasher, that he would have put a P-trap and vent for it. "IF" he did, you should be able to use it.

You would use a reducer bushing in the stub out and connect your hose to a short piece of pipe.

But you MUST confirm that there is a P-trap and vent just before that stub out.

After posting the above, I forgot about your 8" versus the manufacturer's 20" dimension. They have that height requirement to keep the drain line from siphoning the water out of the dishwasher. As such, you do need an airgap to keep that from possibly happening.

 

[Golden_Days_Pete]

One would "ass-u-&-me" that if the builder went to the trouble of plumbing a stub out for a dishwasher, that he would have put a P-trap and vent for it. "IF" he did, you should be able to use it.

You would use a reducer bushing in the stub out and connect your hose to a short piece of pipe.

But you MUST confirm that there is a P-trap and vent just before that stub out.

After posting the above, I forgot about your 8" versus the manufacturer's 20" dimension. They have that height requirement to keep the drain line from siphoning the water out of the dishwasher. As such, you do need an airgap to keep that from possibly happening.

Thanks! My building is 20 years old, and I don’t know how to verify if a p-trap and vent are buried in the wall. It seems it would be unusual to put a p-trap in a cement wall, so I think there likely isn’t one. I also noticed that for the kitchen and guest bath sinks, there are also unused 1.5” drain stubs 8” above grade. The real drains are a foot higher. While I live in FL, I bought this condo as an investment Airbnb property in Puerto Rico, where some builders are iffy. My guess is the builder incorrectly put all the drain stubs at 8” above grade; and the plumbers ended up doing drains that were much higher.

Thanks for explaining the reason for the 20” height. I think between that issue and being unsure of a p-trap, I will shift to trying to tie into the sink drain line. One benefit is I could shorten the unused stub-out, which would help because it’s blocking me from getting the front of the dishwasher flush with the rest of the counter. It’s sticking out by 2” because the stub is using 3” of space in the rear.

If the stub isn’t usable for this, I don’t think it’s usable for anything. Like the stubs in the sinks were never used, one of which is now 1.2"L and the other is 1.5"L. Is there any issue with me cutting the stub from 3” to about 1” or 1.5” other than it might make that stub less easy to use in the future?

 

[MicEd69]

You mentioned earlier that the stub out was "sealed" with duct tape. That's OK for a temporary seal, but it really should be something more permanent if it isn't being used. And I wouldn't worry at all about using it in the future. I'd cut the stud out flush with the wall and install a 1 1/2" test cap in the pipe.

Depending on the dimensions of your sink drain piping, you may have to modify it slightly to get the dishwasher tailpiece installed, but that should be relatively easy. It should look something like this.

 

[Mitchell-DIY-Guy]

You really DO need to cut a hole in your cabinet such that the dishwasher drain line can go in and make a "high loop" and then down to the drain attachment ABOVE the P-Trap as @MicEd69 has shown. If you don't have the high loop, you can have problems. Some jurisdictions (this may not be a concern to you) require the dishwasher "air gap" device mounted in your countertop. This would negate the need for the high loop. The image below shows no cabinetry between the dishwasher and the sink base. My father's old house has this, with site-built cabinets. But normally you'll have a cabinet wall on the sink base. I've seen the drain entry enter LOW, and then "hung high" with a loop and tie-wraps or similar. It's just easier to drill high and then the high loop cannot possibly go away.

 

[Golden_Days_Pete]

Depending on the dimensions of your sink drain piping, you may have to modify it slightly to get the dishwasher tailpiece installed, but that should be relatively easy. It should look something like this.

That’s very helpful. I unscrewed the bottom of the tailpipe, but I haven’t been able to unscrew the top of it because when I twist it with a wrench, it turns the whole basket strainer, not the nut. I’m solo here so I’d have to pay my cleaning woman to hold the strainer in place while I turn the nut. She’s nearby, so I can do that. But I’m wondering if it would be better to leave that connection in place, and instead cut off the bottom 2/3rds of the tailpipe, then connect a part like this to the tailpipe on top and to the T on bottom?
Oatey 1.5 in. x 8-3/4 in. Branch Tailpiece Plastic Slip Joint HDC9698 - The Home Depot

One issue might be that the tailpipe is only 2" or 3” as the photo below shows. When everything is screwed in, only 2” of tailpipe is visible and 1” is inside the T. But the dishwasher branch in the Oatey part likely starts further than 2” down. The only other branch tailpipe the HD here sells is this one, but the branch also seems to be below 2”:
Oatey 1-1/2 in. x 8-1/4 in. Plastic Slip-Joint Sink Drain Tailpiece with High-Line Branch HDC9818 - The Home Depot

So maybe I need to unscrew and remove the current tailpipe? But looking at the Oatey graphic below, it seems like that part isn’t even meant to screw directly into a strainer. Is that right? Or is the graphic only showing 1 way of doing it and screwing it directly to the strainer is also fine? If the Oatey part can’t do that, do other branch tailpipe parts exist where the top end of it can attach directly to the strainer and the bottom attaches to the T?




The same page at HD for the product shows this graphic in which it seems like the piece is screwed directly onto the strainer:



This photo shows the whole strainer connection. Also I don't think I can lower the tailpipe, T or drain because it's only horizontal from the P trap to the wall opening, so lowering it would make the drain pipe slope upwards.

 

[MicEd69]

I've not used one of these before, but I have seen these dishwasher wyes installed in the horizontal line between the two sinks with the dishwasher connection pointed towards the tee. That tee must be a baffled tee to avoid splashing up into that sink section when the dishwasher discharges. You still may need to replace some of the drain piping to fit this properly.

 

[Twowaxhack]

https://www.homedepot.com/p/Dearbor...VzlN_AB1hvQUzEAQYBiABEgK7nfD_BwE&gclsrc=aw.ds
Might need an extension also, wide sink.
https://www.homedepot.com/p/Oatey-1...VGkl_AB1mjgg9EAQYAiABEgJtnfD_BwE&gclsrc=aw.ds

 

[Golden_Days_Pete]

Might need an extension also, wide sink. ...

Very cool product. So I think basically the branch tailpipe would also function as the T, and connect directly to the p-trap and the strainer. While HD says it’s not available for delivery where I am, I’ll find if it or something similar is available at the plumbing supply store. Is it fine to connect a plastic nut onto male metal threads at the bottom of my strainer, or should I buy a separate metal nut for that? Thanks

 

[Golden_Days_Pete]

I've not used one of these before, but I have seen these dishwasher wyes installed in the horizontal line between the two sinks with the dishwasher connection pointed towards the tee. ...

Thanks. That’s a great option. I’ll call the plumbing supply store to find if they have anything like that. I need to decide if I should use my sink water supply for these reasons: 1) the unused inlet stub lacks a shut-off. If I add one, I'd have to cut a 6" x 6" hole in the rear side of the sink cabinet so it can be reached. But people would have to lay on the ground, and be part-way in the cabinet to reach it. And most aquintances doing me an urgent favor won’t be keen on lying on the floor. 2) Under the sink people can more easily notice if the connection is leaking. The base of that cabinet is in bad shape so water leaking there won’t really damage it more than it already is. 3) the stub is 2” off the wall, and I need to reduce it to 1 1/4” for the dishwasher to be flush.

HD sells this narrow valve - BrassCraft 1/2 in. Nominal Inlet x 3/8 in. O.D. Comp x 1/4 in. O.D. Dual Outlet Dual Shut-Off 1/4 in. Turn Angle Ball Valve KTCR1900DVX R1 - The Home Depot that seems to be about 1” thick. How short can I cut the stub to and still attach a valve like that?

On the flip side, I don’t know how hard it would be to connect to the sink’s hot inlet, which is in the picture below. Would I remove the existing shut-off and replace it with a dual shut-off like in graphic below, then re-connect the faucet water line to one valve, and the dishwasher hose to the other? Can you or anyone else tell from the photo what width the hot water inlet stub is, and what size connection the existing sink hose uses? I’d have to know those to buy the correct dual valve. Besides the two questions above, if you or anyone else have any other thoughts or ideas, I’d be glad to hear them.

 

[TomFOhio]

Borrow a large wrench and back up the basket strainer on the threads and then take that tail piece nut loose. Then you can use the
dishwasher wye that you showed us.

 

[MicEd69]

Just get a 3/8" compression tee and keep the existing single shutoff valve under your sink. I wouldn't worry about adding a second valve to the dishwasher, but if you want one, just add a 3/8" compression valve to the line to the dishwasher.

 

[Twowaxhack]

Better than nothing maybe. Always use plastic ferrules with 3/8 plastic tube, IMO.
https://www.amazon.com/Tee-Stop-Val...3&psc=1&mcid=96db1e320b0330f5b17a69f71d9a3eb1

 

[Golden_Days_Pete]

Borrow a large wrench and back up the basket strainer on the threads and then take that tail piece nut loose. Then you can use the
dishwasher wye that you showed us.

I got it loose. I think I’ve made good progress. I had an idea of shortening part of the T at the bottom where it goes into the p-trap. I cut about 3/4” off of the bottom of it, and it still was long enough to have 2” of it to go into the p-trap. Also below the strainer, I used a tailpipe that’s a 1/2” shorter. Those seem to have bought me enough space to fit the regular HD branch tailpipe. Here’s the photo of what it looks like now. Do you or anyone else think it looks good, or should I change anything?

 

[Golden_Days_Pete]

Just get a 3/8" compression tee and keep the existing single shutoff valve under your sink. I wouldn't worry about adding a second valve to the dishwasher, but if you want one, just add a 3/8" compression valve to the line to the dishwasher.

Thanks. My local HD has a compression tee that’’s 3/8 x 3/8 x 38 - is this what you mean: https://www.homedepot.com/p/Everbilt-3-8-in-OD-Compression-Brass-Tee-Fitting-800749/207176761

Or do I need the one that’s 3/8 by 3/8 by 1/4 - Everbilt 3/8 in. x 3/8 in. x 1/4 in. OD Compression Brass Tee Fitting 800949 - The Home Depot

Would I cut the black inlet hose going from the existing shutoff valve to the sink, then attach the 3/8" compression to both sides of that hose, and connect the dishwasher line to the 3rd opening in the tee? Or a different approach? Here's the current set up again so you don't have to scroll:

 

[MicEd69]

Good job! Looking good!

 

[Mitchell-DIY-Guy]

From that photo I sure hope it’s a GFCI protected outlet…

 

[Twowaxhack]

As long as the outlet isn’t facing “ up “ is all that matters there I believe.

 

[MicEd69]

As long as the outlet isn’t facing “ up “ is all that matters there I believe.

Nope, the direction of the receptacle has absolutely no bearing on whether or not a GFCI is required. And if that receptacle is used by the dishwasher, a GFCI is definitely required based on at least the 2017 NEC.

The 2017 NEC, and earlier version as well, has the "6 ft. from the top inside edge of the bowl of a sink" GFCI requirement unless a cord has to pass through a floor, wall, ceiling or fixed barrier. The 2017 NEC included "without passing through a door", but the 2020 NEC removed that phrase, which makes that a requirement for receptacles underneath the sink. The 2020 NEC therefor means that garbage disposals now require a GFCI if they are plugged in and not hard wired.

The 2020 NEC may not be in effect in all jurisdictions. But as all inspectors, whether they be plumbing or electrical, have their own interpretations of code requirements, a jurisdiction is using the 2017 NEC or older, doesn't mean that the electrical inspector won't still require that outlet to a GFCI.

 

[Twowaxhack]

Nope, the direction of the receptacle has absolutely no bearing on whether or not a GFCI is required. And if that receptacle is used by the dishwasher, a GFCI is definitely required based on at least the 2017 NEC.

The 2017 NEC, and earlier version as well, has the "6 ft. from the top inside edge of the bowl of a sink" GFCI requirement unless a cord has to pass through a floor, wall, ceiling or fixed barrier. The 2017 NEC included "without passing through a door", but the 2020 NEC removed that phrase, which makes that a requirement for receptacles underneath the sink. The 2020 NEC therefor means that garbage disposals now require a GFCI if they are plugged in and not hard wired.

The 2020 NEC may not be in effect in all jurisdictions. But as all inspectors, whether they be plumbing or electrical, have their own interpretations of code requirements, a jurisdiction is using the 2017 NEC or older, doesn't mean that the electrical inspector won't still require that outlet to a GFCI.

Well there’s nothing plugged into it and I’m still saying it’s not required. I’d bet it’s switched and it’s also old existing work.

Meanwhile in the real world, we have every tank type electric water heater on the market have from 20-30 amps 240v connect with wire nuts on the top of the unit inside a metal bowl. With the entire case on the outside 2’ x 5’ pure metal.