Replacing RV sink with deeper sink, waste line question

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Whipsaw

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Hi all. I have decided to replace the sink in my 5th wheel RV. I cannot find a new sink of the same dimensions, so I will have to modify the counter and cabinet as well as the waste plumbing. I want to go to a single drain instead of this double sink. The biggest issue I am facing is that this sink is very shallow, so I will need to drop the plumbing down a few inches. The best way to do this from what I can see would be to eliminate the drop elbow at the wall corner by cutting the straight pipe then installing a coupler and new elbow without that drop. The first image is the drop that I am talking about. The 2nd image is of the current under sink config. The third image is the waste pipe that I am lowering where it comes into the sink area under the cabinet. Thank you.

plumbingelbow.jpg
rvsink.jpg
plumbingcrossover.jpg
 

wwhitney

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I'm a bit on what the spatial relationship is of the first photo to the third photo. I presume the grey cube (water heater?) is the same in both photos, so the third photo is the opposite side of that grey cube? I.e. there's another horizontal LT90 not shown, and the drain wraps around 3 sides of the cube?

Anyway, looking only at the 3rd photo, the current sequence of fittings starting at the trap and going downstream is:

san-tee (vent at the top) - street LT90 on the drain to go horizontal again

If it would be enough to lower the trap so that its outlet is at the same elevation as the outlet of that LT90, you could instead do:

horizontal (possibly street) LT90 to turn the corner - upright wye (vertical branch is the vent) - 45 on the vent to get it vertical.

Cheers, Wayne
 

Whipsaw

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Hi, Wayne. The pipe running along the water heater in the 3rd photo is the higher portion in the 1st photo.

So, from what you are saying I really don't need to go cutting the pipe way back behind the water heater, I can simply reconfigure under the sink to drop the trap and tie back in at the same elevation as the horizontal pipe? That's why I came here! I was overthinking things and that would be much easier.
 

wwhitney

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If I'm following correctly, the horizontal sink drain has at least two places where it drops, first (upstream) the one in the 3rd photo under the sink, and second (downstream) the one in the first photo.

Anyway, just looking at the 3rd photo, yes you can reconfigure the portion shown there to eliminate the vertical offset and just pull the vent off the horizontal drain, rather than using a san-tee for pulling the vent off. You'd want to get the fittings on hand (street LT 90, wye, and 45) and check if the street LT90 going into the upright wye would fit upstream of the existing cleanout, or if you are better off replacing the existing cleanout. In the latter case you might want a street wye (or not), and you might want to rotate that cleanout up 30-45 degrees.

Actually if you take measurements, it's possible to calculate using the dimensions in the Charlotte Pipe catalog what will fit. If you use the back of the cabinet as a plumb reference plane , what's the horizontal distance from there to the middle of the trap arm (the horizontal drain between the trap and the san-tee), and to the near edge of the hub on the cleanout?

Cheers, Wayne
 

Whipsaw

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Hi Wayne.

It's 3 1/2" from the back of the cabinet to the center of the trap arm. It is 10 3/4" to the near edge of the hub on the cleanout. I have attached a pic of where I would cut the existing plumbing to retrofit per your first response.

modifiedplumbing.jpg
 

wwhitney

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I'm assuming that everything in the picture is 1-1/2" ABS. [BTW, I'm still not clear on picture 1 in relation to picture 3; are the two sides of the heater shown in those pictures adjacent, so 90 degrees apart? I.e. the heater is under a corner cabinet?]

For the current location of the trap arm, you have 7-1/4" to the cleanout. A street LT90 would take up 3-1/2" of that, and a regular wye would be another 4". So if you cut 1" to the left (upstream) of the current cleanout, your horizontal drain at the back of the sink base would end up moving back 1-1/4".

That might be OK, or it might be better to cut after the cleanout and replace the cleanout. Your trap configuration is going to change anyway with the new sink, so the main think is to confirm that the new sink's depth will work with the elevation of the lower horizontal drain in picture 3. Then you can remove the trap and upstream, swap in the new sink, and then figure out how to connect the new trap to that lower horizontal drain and the existing vent. Or if the vent is an AAV, you might move the AAV.

Cheers, Wayne
 

Whipsaw

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I'm assuming that everything in the picture is 1-1/2" ABS. [BTW, I'm still not clear on picture 1 in relation to picture 3; are the two sides of the heater shown in those pictures adjacent, so 90 degrees apart? I.e. the heater is under a corner cabinet?]

I'm sorry I wasn't more clear. Yes, it is a corner cabinet and there is a 90 degree elbow (sweep?) to make the turn around the heater to get to the sink plumbing. Here's a pic:

90turn.jpg
 
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Whipsaw

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For the current location of the trap arm, you have 7-1/4" to the cleanout. A street LT90 would take up 3-1/2" of that, and a regular wye would be another 4". So if you cut 1" to the left (upstream) of the current cleanout, your horizontal drain at the back of the sink base would end up moving back 1-1/4".

That might be OK, or it might be better to cut after the cleanout and replace the cleanout. Your trap configuration is going to change anyway with the new sink, so the main think is to confirm that the new sink's depth will work with the elevation of the lower horizontal drain in picture 3. Then you can remove the trap and upstream, swap in the new sink, and then figure out how to connect the new trap to that lower horizontal drain and the existing vent. Or if the vent is an AAV, you might move the AAV.
Yes, it's all 1 1/2" save for the crossover piece coming from the sink which appears to be 1 1/4" going into a reducer coupler. I think what I am going to do is buy the sink, all the fittings you listed, a piece of pipe, a new strainer and tailpiece and install the sink then see where I am at. Like I said, it's only 2" deeper, and if I can tie into that horizontal line which is more than 5" below the current tie in of the p-trap then it's hard to imagine how it wouldn't be feasible from an elevation standpoint. The new single tailpiece will allow me to adjust the height.

I thank you. I really appreciate you taking the time and I will come back to post my progress. I do have to expand the hole for the sink, too, so a little more prep than usual.
 

WorthFlorida

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Just another though, if you are replacing it with another double bowl sink this trap configuration may work. Connect the trap arm to the location of the clean out. From the clean out to the vent will need to be redone. A wye will be needed in this configuration, not a sani-tee. However, you may lose some usable space under the cabinet.

Screen Shot 2022-04-20 at 6.22.59 PM.jpg
 
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