TOTO ST412M Skirted Toilet Leak

Discussion in 'Toilet Forum discussions' started by madmax6661, Sep 20, 2020.

  1. madmax6661

    madmax6661 New Member

    Sep 20, 2020
    Hello Forumers,

    I have a Toto ST412M tank mounted on a CT412F bowl so it's a two-piece skirted toilet. It was running smoothly without any leaks until I decided to install a handheld bidet sprayer for various reasons. On most regular toilets, this wouldn't have been a difficult task because of the easy accessibility presented by the tank's fill valve to connect the T-adapter for the bidet sprayer. However, due to the design of a skirted toilet where the fill valve is concealed behind the toilet, I had to purchase an extension hose to extend the fill valve outside the toilet where I could connect the T-adapter properly.

    Now, to connect this extension hose to the tank, I was forced to unscrew and unmount the tank from the bowl. After then connecting the extension hose, I proceeded to mount the tank back using the screw/bolt assembly (image 1) and here is where my problems began. After turning the water supply back on, I observed leaks from both the mounting holes (image 3) which still refuse to stop, despite various things being attempted:
    1. Adjusting tightness for either bolt assembly
    2. Using a spirit level to ensure the tank is level and re-mounting it before re-tightening the bolts
    3. Disassembling and re-assembling the mounting assemblies to ensure uniformity and correct fit
    4. Swapping the mounting assemblies from their original positions
    5. Adjusting/moving the tank laterally numerous times to align tank bolts with bowl screws
    6. Applying teflon tape to the bottom half of the bolts to, once again, ensure a snug fit
    7. Repeatedly cursing my decision to install the handheld sprayer and listlessly hoping for a leak-free toilet
    The bolt assemblies themselves seem to be fine, although each rubber O-ring (see image 2) appears to have just a wee bit of warping where they present the seal on the mounting holes. This caused me to think of replacing the O-rings but these have been unavailable at a few hardware stores I've contacted, include The Home Depot, Ace Hardware & a local plumbing store. No luck online either. With my novice knowledge on leak-fixing coming to a standstill, I'm seemingly running out of ideas and options to try and plug it. Fortunately we have a second bathroom that can be used while this one's out-of-service.

    I would appreciate any advice or insight anyone can provide, as to what else can be done to stop these leaks. I would hate to hire a plumber for such a small issue and throw away money.

    Thank you in advance!


    Attached Files:

  2. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Sep 2, 2004
    Retired Systems engineer for defense industry.
    New England
    Make sure that you have the tanks sealing rubber washer in the right place. The bolt goes through the rubber washer, and then that goes through the tank. Then, on the bottom, there's a metal washer and the nut.

    The tank should be nearly touching the bowl when it's installed properly. Since the porcelain isn't elastic, I tend to use a sheet of paper under each positioning lug, then carefully, a little bit on each side evenly, tighten the nuts until I can just pull the paper out with some resistance. If the metal washer is installed on top of the rubber one, then the bolt is inserted, you can get leaks.

    If the area where the rubber washer tries to seal is rough, a piece of fine sandpaper or emery cloth can be used to smooth it out prior to installing the bolt and rubber washer.
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  4. Weary_landlord

    Weary_landlord New Member

    Jun 14, 2015
    Sandeep did you solve this?
  5. Terry

    Terry Administrator Staff Member

    Aug 17, 2004
    Bothell, Washington

    The tank to bowl on the Aquia may need new rubber washers if you pull and reset the tank. Those are getting hard to get from TOTO.
    The bowl has threaded studs mounted to the bowl that the tank drops over.
    Then it's rubber washer, metal washer and then screw top threaded down.
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