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Thread: What's Causing My K-3402 PB Rialto Toilet to Leave a Black Residue in Tank & Bowl?

  1. #1
    DIY Junior Member BillMPerry's Avatar
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    Jun 2010
    East Aurora, NY

    Default What's Causing My K-3402 PB Rialto Toilet to Leave a Black Residue in Tank & Bowl?

    I have a K-3402 PB Rialto Toilet, and there is a black residue collecting in the tank and around the rim of the bowl. If I had to guess, I'd say it's the flapper or flapper seal breaking down. Our water isn't particularly hard. And I recently replaced the flapper. But, I'm still seeing the residue in the tank and rim of the bowl. Whenever I clean up the residue it returns within a day or so.

    Does anyone have any thoughts on what might be causing this residue to collect? And, most importantly, how might I go about fixing the problem?

    Thank you very much for the help.

  2. #2
    Retired Defense Industry Engineer jadnashua's Avatar
    Join Date
    Sep 2004
    New England


    Hose from the shutoff to the toilet?
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  3. #3


    Another possible cause is iron and manganese in the water supply. The linked information is several years old but it's a relevant and concise explanation of common symptoms and solutions for the problem you describe.

    Hope this helps.

  4. #4
    Master Plumber-Gas Fitter shacko's Avatar
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    Jan 2006
    Rosedale, Md


    Are you using those inside tank cleaners? on some toilets they are a no no, they cause the parts to break down.

  5. #5
    Engineer pwjone1's Avatar
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    Apr 2009
    Poughkeepsie, NY


    OK, as someone that just tore down a Rialto, one source of Black residue in the tank and therefore the bowl is from the fill valve base. The rubber washers at the bottom are black, feel around there, it they get old enough, right water conditions, you'll see some black as the rubber disintegrates. Generally the rubber gasket at the flush valve, depending on the model, could also be black rubber, but I'd say red is more frequently the case there, just depends. And I generally never have used inside tank bowl cleaners, but definitely have seen the rubber disintegrate, anyway. Just age.
    Paul Jones

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