Amateur Kitchen Sink Replacement - Double Bowl to Single, to cap or not to cap?

[FatDanderson]

Hi all, new here. I'm planning to replace my kitchen sink going from a double bowl with a garbage disposal to a single bowl (drain on the left side) keeping the garbage disposal. My plan has been to simply cap off the other drain. I've attached a picture with my plan of action and I've even purchased a 1-1/2" schedule 40 cap and some pipe thread sealant.

This seemed all well reasoned to me, though I keep reading in various plumbing forums that "no self-respecting plumber" would do it that way. I suppose the proper way would be to get a 90 degree disposal elbow and go right into the p trap? That would be quite challenging for me given the big ole ro holding tank in the way, plus I'm pretty sure it wouldn't line up even if I swing the p trap toward the disposal and there is no way I'm comfortable messing with the SanTee. My question for you all is, given that I'm not a self-respecting plumber, is it fine to go with my plan and just cap that spare drain line? Is there something I'm missing that makes capping that really problematic? I'm guessing even though it isn't the plumber approved "right way" to do it, that really it's fine and won't give me any problems. What say y'all please?

 

[Reach4]

Oatey 1-1/2 in. x 15 in. White Plastic Slip-Joint Sink Drain Outlet Waste Arm HDC2690B - The Home Depot

The 1-1/2 in. x 15 in. Plastic Tubular Waste Arm features polypropylene plastic construction and the option for either slip joint or direct connection. Designed for use in tubular drain applications. Available in white or black. Oatey products have earned the trust of plumbing professionals for...

www.homedepot.com

I think you could use one of those elbows, and feed into the trap.

You would need to cut the elbow to length.

Alternatively, https://www.homedepot.com/p/Oatey-1...Sink-Drain-Elbow-Pipe-White-HDC9675/316369523 may meet your needs.


EDIT: Whoa... I just noticed that your RO feeds in after the U of the trap. Not allowed. That must feed upstream of the trap. Maybe tap your existing port into the tubing before the U, or maybe even feed the RO into the dishwasher port on the disposal.

 

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[FatDanderson]

Oatey 1-1/2 in. x 15 in. White Plastic Slip-Joint Sink Drain Outlet Waste Arm HDC2690B - The Home Depot

The 1-1/2 in. x 15 in. Plastic Tubular Waste Arm features polypropylene plastic construction and the option for either slip joint or direct connection. Designed for use in tubular drain applications. Available in white or black. Oatey products have earned the trust of plumbing professionals for...

www.homedepot.com

I think you could use one of those elbows, and feed into the trap.

You would need to cut the elbow to length.

Alternatively, https://www.homedepot.com/p/Oatey-1...Sink-Drain-Elbow-Pipe-White-HDC9675/316369523 may meet your needs.


EDIT: Whoa... I just noticed that your RO feeds in after the U of the trap. Not allowed. That must feed upstream of the trap. Maybe tap your existing port into the tubing before the U, or maybe even feed the RO into the dishwasher port on the disposal.

Thank you very much for your reply Reach4. Per your response, I've come up with a new plan of action:

Does that seem like a good way to tackle this? I just had the RO system installed professionally a few months ago. I have half a mind to call them up and have them come fix this, but I'll probably just take care of it since I'll be messing around under there anyway. Thanks for flagging that!

If you don't mind answering, I have two questions just to better my own understanding.

1. What is the actual problem with capping the extra line, as I initially wanted to do?
2. What is the reason the RO shouldn't feed in after the U please? If I ever deal with this water guy again I might want to educate him. I assume it isn't up to code this way, but do you know why?

My sincere thanks again.

 

[Reach4]

Looks good.

1. For capping, there is probably something made for the purpose, and would be OK. It would not be schedule 40. The drain stuff is slip joint tubular, and the OD is 1.5 inches for 1.5 inch nominal.

Schedule 40 is significantly bigger, and you usually use glue. Cannot glue to slip joint tubular.

So capping should be OK, but you have to find the right thing, and it could look hokey. I am not a plumber.

2. The purpose of the trap is to keep sewer gases and smells trapped. Your setup could give free flow of sewer gas up and out your air gap. If you do not have an air gap, it still would not be right, but I cannot provide an argument that is as clear and logical.