Fixing Leaking Toto Washlet S300 / S350 Junction Valve

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Intro: Fixing Leaking Toto Washlet S300 / S350 Junction Valve

Is your Toto Washlet S300 / s350 Junction Valve leaking at the tank connection?

I had this problem and tried many different combinations of fiber washers, o-rings, conical rubber gaskets, flat brass washers, sealant tape, metric thread adapters, etc. All to no avail. The final configuration that worked was not intuitive, but is absurdly simple.

TLDR; Go get a variety pack of washers at the hardware store and add an extra thin FLAT brass washer to the mix.

Step 1: The Official Toto Instructions Say to Use Only Flat Fiber Washers to Seal

The official Toto instructions DID NOT WORK in my case.

If the connection to your tank float intake end is PERFECTLY FLAT, then you might be able to follow the official Toto instructions and have the fiber washer alone seal correctly.

I even purchased a new toilet tank float intake and another valve set thinking my original THU9339 Junction Valve was defective, that the THU9340 Fiber Washers were bad, and/or that I had stripped the threads on the old float assembly.

Step 2: Inspect the Fill Tank Connection End

If the fill connection to the tank float intake is CONICAL on the inside, then you may need to install an extra gasket to avoid leaks.

Skip ahead for the solution, but for those who are interested, here is what I tried:

  • I reseated the connector, careful to not cross-thread or strip the plastic tank connector. Still leaked
  • I added thread-sealing tape and tightened the female nut down with a crescent wrench as tight as I could. Still leaked.
  • I tried using a flat rubber washer on top of the fiber washer. I barely could get the threads to grip and it still leaked.
  • I used a conical rubber washer that fit perfectly inside the bevel of the tank connector but could not even get the thing to grab the threads (too far away).
  • I removed the fiber washer and tried the conical rubber straight against the flat brass insides of the T connector. Still leaked.
  • I bought a new tank float as the threads on the old one were a bit mangled by now. Still leaked!

  • I bought a NEW Toto T connector and repeated the above steps. STILL LEAKED!

By now I had purchased every kind of adapter and type of washer I could find and had brand new parts to test without having to be upside down wedged between the wall and toilet.

I'm still blown away that Toto would provide such a user-unfriendly valve and completely inadequate instructions. But I digress... :)

Step 3: Use an Additional FLAT Brass Washer on Top of the Fiber Washer

*** Add an additional FLAT brass washer on top of the fiber washer. ***

Instead of following the official Toto instructions:

Junction Valve > Fiber Washer > Tank Inlet...

It should be:

Junction Valve > Fiber Washer > Brass Washer > Tank Inlet

This creates a flat surface for the toilet tank inlet to sit on without adding so much space that the nut cannot be screwed on far enough to seat correctly.

Now attach the Junction Valve to the toilet tank as normal.

THAT'S IT!

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The fiber washers work by expanding slightly when they contact water, creating a seal that won't crack and leak like rubber washers do over time.

Just hand tightening made a good seal, but I added a 1/4 turn with a wrench to make sure. I did not use any teflon tape in any parts of the assembly. I've read that teflon tape is only to be used in non-compression fittings.

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UPDATE 2018-08-05:

@chjwolters mentioned not using the fiber washers at all, seating the tank connector directly against the flat brass insert inside the gray plastic 'T'.

I think the key to success here is having a good surface for the plastic connector to seal against. I noticed that my fiber washer had a ring dented in it from the beveled edge of the tank connector, which gave me the idea of the brass washer. The brass washer might even out the pressure, allowing the fiber washer to do its thing.

@LeetPete successfully used "a combination of a flat rubber washer followed by a cone washer" to stop the leak. Perhaps the rubber cone that came with my variety pack was simply too tall.

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    14 Discussions

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    LeetPete

    3 months ago

    I'm so thankful for this thread! I just purchased the Toto S550e and am having the exact same leak problem! So far I've tried the washer that comes with the washlet and not using a washer at all, but no luck. I'm going to go to Lowe's tomorrow to buy a brass flat washer. I really hope this fixes the problem. Such a shame that Toto doesn't include some sort of solution in the box, especially for such a high-end bidet.

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    LeetPeteLeetPete

    Reply 3 months ago

    Update: I fixed it! Adding a brass washer didn’t do it for me though. I had to use a combination of a flat rubber washer followed by a cone washer. This was the only combination that would make the connection between the tri-connector and the tank inlet tight enough. I hand tightened it and then used a wrench for a little more tightness at the end. Ultimately, this ordeal cost me several hours of time, some back pain, and $7 that I spent for a variety pack of washers from Lowe’s.

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    StevenS381LeetPete

    Reply 6 weeks ago

    LeetPete, thanks a ton for your advice on this.

    I too purchased a S550e and encountered this leak issue during installation. I was close to calling a plumber but decided to use your idea to combine the flat rubber washer (the official Toto one included with the box) followed by a cone washer. It worked!

    For those wondering what cone washers I used, here's the home depot link: https://www.homedepot.com/p/DANCO-Assorted-Cone-Wa...

    Now my Toto S550e is working like a charm. I hope Toto is able to address this issue since it seems like many customers encounter this leaky pipe.

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    SemiconductedLeetPete

    Reply 3 months ago

    Thanks for sharing your solution!

    That method still leaked with my particular setup, though the water pressure in our building is also industrial-strength.

    Was the rubber cone washer you used the thick, flat-bottomed kind or the 'floppy' thin red ones? The flat-bottomed rubber cone washer in my variety pack may have just been too tall to allow the threads to seat properly.

    Most of all, glad you were able to solve it. :)

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    chjwolters

    Tip 7 months ago on Step 3

    I had the exact same problem but what worked for me was not using any washer at all. For some reason, this was the last step I took after days of trying everything. I guess I am not used to not needing a washer or a rubber seal but in the case of this piston type valve, the right pressure in the right place seems to work.

    1 reply
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    Semiconductedchjwolters

    Reply 3 months ago

    Glad to hear you were able to solve it and thanks for the additional technique.

    I noticed there is a flat brass coupling the gray plastic to the free-spinning chrome female nut. In your case, it seems that was enough to create a good seal.

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    DougD65

    Question 6 months ago on Step 3

    Hi. It was great to find your post. Did you hand tighten after you installed the brash washer or tighten further with a wrench? I installed a C200 yesterday and was having some leaking at the same spot. I tightened very tight with a wrench. It stopped the leaking but I'm now worried that I perhaps over-tightened, which will cause an issue in the future. Thoughts?

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    SemiconductedDougD65

    Reply 3 months ago

    I say if it works as it is, leave it alone! :)

    However in general, overtightening can add extra stress when the metal expands and contracts with temperature changes. Also, the elastomers in the plastic connector degrade over time, making it more brittle and prone to cracking.

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    SemiconductedDougD65

    Answer 6 months ago

    I hand tightened as much as I could go and left it at that. I may have use a pipe wrench for the last 30º or so.

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    Yveslespins

    Question 3 months ago

    I'm trying to install my new s500e but the water connections aren't easy. Is it possible that the thread in Toto provided connecting pieces be different in Japan from the thread we use in America? It should normally be easy to achieve the major part of the connections by hand as it is brand new material but I find that it gets difficult almost from the beginning.Thereby my question about the pipe connection thread.

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    SemiconductedYveslespins

    Reply 3 months ago

    I thought the threads might be Metric (like all modern products SHOULD be) but mine really seemed to be Imperial. I tested it at the hardware store against every connector I could find and also bought a brand new float assembly as I thought the leak may have been due to stripped threads on the tank inlet / float connection.

    The closest known Metric connector I found had much finer threads - though the Toto could actually still be Metric with a pitch that is very very close to the Imperial version.

    Hand tightening alone was enough to keep it leak-free, though I did use a wrench to add an extra 45º-90º turn.

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    FoxfairH

    Tip 5 months ago on Step 1

    The installation guide is simplified enough to let most owners ignore the installation order which is critical. I had the same problem on my C100 washlet and had installed it several times. Finally I found that you have to install the connection of *wall* water supply hose to the junction valve first (the bottom), the hose to the washlet(middle), then the tank short inlet to the junction valve(top of the 3-point). An advantage of installing in this way is that you can keep watching if the top part is installed vertically straight. You may need several times to get it right, just be patient.

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    jenster27

    Question 6 months ago

    So glad to find this thread! At my wits end over here with the Toto C100. Same leaking problem. I've tried the flat washer--that made the leak worse for me. Tried no washer--that was better at the top of the tank inlet. But now, it looks like the water is leaking between the top nut and the gray plastic diverter piece on the Toto part. Starting to wonder if the part itself is damaged--there seems to be a lot of give and sliding on the part. Any suggestions before I send away for a replacement diverter piece?

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    Semiconductedjenster27

    Answer 6 months ago

    The leak you describe was the main problem I was having. I'd check to make sure the plastic threaded inlet tube is FLAT on the bottom and not damaged from messing with it. The fibre washer is meant to expand and seal, though needs a flat surface putting pressure on it. For me, that's where the 3rd-party flat brass washer came into play. I hope this helps and you are able to fix it. So frustrating! :)