What is going on with this dishwasher drain tube?

[ThereGoesPlanB]

I'm just starting the process of remodeling my kitchen, partially spurred on by a dishwasher that stopped draining. While removing the dishwasher and it's drain tube, I was a bit perplexed at the existing plumbing. This first picture shows the drain tube entering the sink base cabinet and extending up above the drain:

Rather than go into the garbage disposal, there is a an open waste pipe that it's shoved down:

Here is a somewhat blurry picture of the rest of that waste pipe:

So that waste pipe exits through the back of the wall below the main sink waste pipe. I only have one drain pipe entering the crawlspace at this location, so presumably it's connected to the main sink drain in the wall.

So my questions:
1) Is this up to code? If not, are there issues with this arrangement besides code violation?
2) Do you see any reason why the original owners/builders didn't use the garbage disposal? I'm almost certain this arrangement was created when the house when the house was first built.
3) What should I do with this pipe when I replace the cabinets and put in the new dishwasher? Can I just cap it off at the wall and route the new drain pipe to the disposal?

 

[Reach4]

That is called a standpipe. It is supposed to have an airgap as illustrated in the first illustration in https://www.sos.state.co.us/CCR/GenerateRulePdf.do?ruleVersionId=2141&fileName=3 CCR 720-1

I don't know when the airgap rules were put into place. It was common and permitted at some time in the past do not have the airgap. Your standpipe may predate the requirement.

You could cap it if you don't use it.

 

[Sponsor]

 

[WorthFlorida]

Original post deleted. Yes it is legal. The trap is glued in, so on the remodel you’ll need to cut the p trap almost at the wall so you can remove and install new the cabinets. When the cabinet is removed you may have to open the wall to rework the drain so there is sufficient pipe extending into the new cabinet to install a new trap. Just note that not to extend the DW hose down too far into the pipe.

 

[Jadnashua]

I don't see any reason to have to modify where it's connected, but the end of the DW hose could be anchored above the top of the standpipe, and angled down into it to provide a second air gap. In reality, it's better than connecting it to the knockout on a garbage disposal, since the height of the standpipe would almost certainly keep the waste level below the end of the pipe and has an air gap. As long as it isn't poked down into the p-trap, it should be fine. Because the top of the standpipe is not sealed to the DW drain hose, if the line did backup, there'd be no pressure to push it back into the DW, it would overflow the standpipe.

Commercial DW often discharge into a floor basin with an air gap. Your standpipe is providing that function unless there's a backup in the drain since the water level is typically only in the p-trap below. If there were with a garbage disposal, or a tailpiece on the sink pipe, it would too. This is why they call for air gaps which you can provide by clamping the hose above the rim of the standpipe. Essentially, you have an air gap in your current installation - the DW hose is not sealed to the standpipe...there is an air gap between the two.

The only other issue I see is if you didn't use the DW often enough, and the trap dried out. But, that's true of any fixture...left long enough, the trap water will all evaporate, whether that be a sink, washing machine standpipe, or whatever. My vote, leave it alone...