Extending cast iron drain line for pedestal sink

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jak85

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The drain line for my bathroom sink is 14.5" off the floor, roughly 20" from the center of the toilet flange and about 30" to the door on the left. Since I've changed the bathroom door to an outswing, I'd like to move the sink over maybe 4-6" so there is more room between the sink and the toilet.

It seems pretty straight forward to extend the cast iron pipe, I'd just buy a PVC adapter and run the pipe a few more inches using PVC. My main area of concern is raising the height of the drain line to about 25" as per the installation manual for the Kohler Cimarron pedestal sink I intend to buy. Is it acceptable to elbow straight up from the end of the cast iron pipe about 10" and then elbow straight out of the wall from there?
 

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Plumber69

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The drain line for my bathroom sink is 14.5" off the floor, roughly 20" from the center of the toilet flange and about 30" to the door on the left. Since I've changed the bathroom door to an outswing, I'd like to move the sink over maybe 4-6" so there is more room between the sink and the toilet.

It seems pretty straight forward to extend the cast iron pipe, I'd just buy a PVC adapter and run the pipe a few more inches using PVC. My main area of concern is raising the height of the drain line to about 25" as per the installation manual for the Kohler Cimarron pedestal sink I intend to buy. Is it acceptable to elbow straight up from the end of the cast iron pipe about 10" and then elbow straight out of the wall from there?
No you can't do that. You can use two 45's come up 10 inches. Put a tee and up another x amount of inches so a autovent is hidden behind a mirror. I think you should be able to do that
 

jak85

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No you can't do that. You can use two 45's come up 10 inches. Put a tee and up another x amount of inches so a autovent is hidden behind a mirror. I think you should be able to do that

I'm not too familiar with autovents, all my drain lines run to the main 4" cast iron vent stack (seen on the far right of the picture), would that not be good enough for ventilation?

Also, since the back of the pedestal is completely opened from the bottom up, does the drain pipe height matter that much? I know in some pedestals there is a partition that runs a third of the way up the back which could block the P trap installation, but that doesn't appear to be a problem with this sink.
 

Smooky

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If you turn the pipe up as you suggest, then the existing vent pipe in the wall is useless for that sink. The trap can be siphoned dry causing sewer odor to enter the living space through the drain on that sink. If you do that you need a vent out the roof or up and over to the existing vent. As mentioned above you could install an Air Admittance Valve (AAV). An AAV allows air into the pipe but does not allow sewer odor out. I would not install it in an inaccessible area such as hidden in the wall or behind a mirror. They do fail and need to be replaced sometimes. Also the AAV has to be in an open area so air can enter the pipe for it to work correctly. Sometimes they are installed in the wall with a little vent cover to hide the AAV. An AAV could be installed under the sink if you have room.

aav_in_wall.jpg


sure_vent_wall_box.jpg
 
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jak85

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Sorry wrong sink I was thinking of. Drain height don't matter. Lower is actually better


That's what I was thinking, but why do you think they call for a 25" height in the instructions? I haven't seen the pedestal in person because it's only available online, but the schematic shows a completely open design on the back.
 

Smooky

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That's what I was thinking, but why do you think they call for a 25" height in the instructions? I haven't seen the pedestal in person because it's only available online, but the schematic shows a completely open design on the back.

Are you sure it is 25"? That seems kind of high.
 

jak85

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Are you sure it is 25"? That seems kind of high.

It's actually 23" to center of drain on the homedepot.com pdf sheet for this model, but then kohler.com shows it being 20.5" for the same model.
 
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