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Thread: Combining sink and toilet's water pipes?

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  1. #1

    Post Combining sink and toilet's water pipes?

    I'm a complete newbie at all this, so please bear with me. I don't know any technical terms whatsoever.

    I live in a 1920s condo building where there's been a regulation to replace all tankless flushometer toilets with ones with tanks. This is because there've been a few occasions where the water's been shut off for whatever reason, and when it's turned back on, some tankless toilets have just kept running. And if the occupant's out of town... well, we've had some massive water bills.

    I've done the research to find a toilet that fits my space requirements, already no easy task (pretty settled on the Toto Guinevere, if anyone's curious). Now there's the issue of how to do the plumbing. Two plumbers are suggesting two different ways, and I have no idea if they're equal.

    The tricky thing is that the water input pipe for the current toilet is too high for a tank, so it will prevent the tank from being aligned parallel to the wall. My next door neighbor has the tank askew, and it looks tacky.

    Option A) Move the pipe input lower. I think this is more expensive, and involves redoing the tile on the wall: breaking in the new hole and fixing up the old one. Sounds scary to me. Plus I don't know how they'd get into the wall. The access panel through my bedroom closet only seems to get to behind the shower, not to the sink or toilet.

    Option B) One other unit in the building's plumber has rerouted the toilet water input so that it draws from the same pipe as the sink, which is just next to it. The new pipe would go through the side of the under-sink cabinet. The current hole in the wall would be somehow sealed off and the hidden by the tank. To someone with no plumbing experience, this sounds fine, and it's already been done and hasn't been problematic, AFAIK. But is it a cop-out? Is A the right way to do it, and is there something else I need to think about it I connect the two?

    Also, the Guinevere is not an insulated tank, and I'm worried about sweating. I've read on the forums about mixer valves, and it seems like it would work well with Option B, since there's hot water to the sink already. Would a mixer valve also work with Option A? More trouble than it's worth? "Depends"?

    So. To summarize:
    - Option A or B, pros and cons, general thoughts?
    - Mixer valve compatibility?

    Thanks so much! This forum has been a great resource already.

  2. #2
    DIY Senior Member Marlin336's Avatar
    Join Date
    Aug 2007
    Suffolk, NY


    For option A you would cut the Sheetrock in your bedroom to access the pipes. This way you can get away without damaging the tiles. I like this idea the best.

    For option B you have to check local codes. Here you have to have at least 3/4 to your last fixture which means you can not tee off half inch for a toilet. It's also going to look pretty tacky having the copper line running out of your vanity and along the wall. It will work fine however. Sealing the current hole can just be done with silicone if it's going to be hidden. I don't know how you would cut the old line out and cap it though.

    I've never even heard of an insulated toilet, some of the toilets in my house date back to the 20s and I don't think I've ever had a problem with sweating causing any kind of damage to the walls or floors.
    Last edited by Marlin336; 10-07-2007 at 03:51 AM.

  3. #3
    Plumber patrick88's Avatar
    Join Date
    Sep 2007
    Webster Ma.


    Also, the Guinevere is not an insulated tank, and I'm worried about sweating. I've read on the forums about mixer valves, and it seems like it would work well with Option B, since there's hot water to the sink already. Would a mixer valve also work with Option A? More trouble than it's worth? "Depends"?
    The mixing valve need to be installed in a place that will not be covered over. You can use an access panel. I have a mixing valve on my toilet and it works great. My floor rotted out from the toilet sweating. I had to replace the floor under the toilet soon after moving into my house. I would open the wall in your bed room and reroute the pipes as needed. I would place the toilet mixer inside the panel behind shower so you can have access to it. You need to be able to get to the mixer because during the colder less humid months you don't need to mix the water. Theses like any other valve will leek at some point so you want to be able to get to it
    I'm just starting to work with an old friend of mine to bring solar electric and hot water systems, wind turbines, Flex Fuel Boilers, batteries, hydroponic gardening, books, pellet grills and more. Also the parts for DIY installation.

  4. #4


    Yeah, after typing all that out and having it clear in my head, it did start making more sense to just do the job right, rather than a stop-gap. Time to check the savings account...

  5. #5
    Retired Defense Industry Engineer jadnashua's Avatar
    Join Date
    Sep 2004
    New England


    A diamond bit or maybe even a carbide bit will cut a nice hole in the tiled wall (if the tile is really from the 1920's, then a carbide bit probably will work). Note that the tile is probably on a floated mud wall and there is metal lath in there, which is a pain to cut through without snagging it and pulling off a bunch of tile with it. Just go slow, with the right tool, and it should go right through.

    In a large building, the water often has a chance to warm up a fair amount before it gets to your toilet, so it may not be cold enough to cause the toilet to sweat. You could try it without the tempering valve first, then add one if needed. If the unit has central air, then that may minimize it as well. Where it is the biggest problem is if the toilet is used repeatedly over a short time, and the humidity is high...this keeps replacing the water in the tank with cold, and eventually, it cools off enough to condense on the outside from all of the humidity. For a toilet that only gets flushed occassionally, it usually doesn't get cold enough to be a problem for condensation, or if it does, it doesn't last long as the water in the tank warms up above the condensation point.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  6. #6


    Well, the latest update from a plumber who's done about 12 other units in the building is that this old building has brass rises, not copper. They go to the apartments above and below me, so they can't cut through that. He said they've been fitting a 1/2" chrome pipe through the vanity, so it may not look that bad, and the space is small anyway. He also said that going through the bedroom wall would increase the working time from 4-5 hours to 1-2 days!

    Apparently the Toto they're recommending has a 10" rough-in and only a 26" depth. I'm not sure which one that is, and he couldn't remember off the top of his head. It's not a Unifit because I brought up the Guinevere I'd been looking at, and he said that it would involve at least another hour to get the adapter bolted down because they'd have to drill into the floor tile. The other thing is that the Guinevere I have my eye on has a depth of 28 1/4". Although it would fit in the space, maybe that's a bit tight. The door swing allows 29", but the door frame is at about 26" (current flushometer toilet only 23 1/2!)

    I realized after he left I forgot to ask about the mixer valve! Oh well, next time he comes around. I also didn't think it was something that could be easily added later, so that helps.

    I am predisposed to liking this plumber because he recommended a Toto as the toilet of choice over any other brand. But does what he's saying makes sense?


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