My toilet's tank has a lot of dark brown scum growing on the walls. I assume it's some kind of mold or bacteria. The water itself isn't cloudy, but when you flush, some of the scum comes loose and gets dragged along. It then clings to the toilet bowl and makes nasty brown stains.

I am too lazy to actually clean the tank, so I though maybe I can get away with just pouring bleach into it. The bleach should (eventually) degrade all the scum and mostly clean up the tank. Then I'll do a few flush to rinse it away and I'm done.

Is this a bad idea to do? I imagine the porcelain tank will not be harmed, but I'm not sure about the plastic parts of the flush mechanism. I'm renting the apartment, so I'd rather avoid having to replace or repair the toilet itself due to bleach damage.

  • 1
    What does your landlord (landperson?) say about it all?
    – Tim
    Commented May 26, 2022 at 6:42
  • 2
    Are you on a well? It sounds like rust accumulation in the tank from hard water. You could try putting an Iron Out tablet in the tank.
    – aphoria
    Commented May 26, 2022 at 12:11
  • 6
    Bleach to excess will damage rubber parts. At reasonable dilutions and not too frequently, should not be a problem.
    – Ecnerwal
    Commented May 26, 2022 at 12:38
  • 4
    I doubt that it bacteria or anything living. Most likely it's just mineral deposits and sediment.
    – JimmyJames
    Commented May 26, 2022 at 16:33
  • 2
    Beware of poseidon's burn ! Commented May 27, 2022 at 8:12

7 Answers 7


This is perfectly normal practice.

I have put a shot of bleach in toilet cisterns as regular maintenance for years.

Just put in a small amount and leave a couple of hours before flushing. Do this two or three times a year.

Where you have a large deposit to remove, you may need to dose the cistern a few days running to get it all clear. This too will not harm the mechanism.

I don't see an issue with it being rented. You are just cleaning the toilet.

  • 5
    Just be careful not to drink the shot out of habit... :-)
    – JACK
    Commented May 26, 2022 at 12:35
  • 38
    @JACK Actually, while I know that was meant as a joke, it is relevant for anyone who's got dogs or cats in the house who might have a propensity for drinking from the toilet. Make sure to close the bathroom door to prevent pets from drinking out of the toilet when there's bleach or any other kind of cleaning chemicals in there. Commented May 26, 2022 at 12:46
  • 1
    @DarrelHoffman Great point!
    – JACK
    Commented May 26, 2022 at 12:55

I also would adhere to the "shot" of bleach is fine. This will not harm the tank or the pipes.

The only other concern would be if you are on a septic tank. Bleach kills the beneficial bacteria in the tank that breaks down the solid waste.


  • 6
    So, do you really think that a shot of bleach going into a 1,000 gallon septic tank is going to kill all the bacteria? Can you provide a reference for that? Thanks!
    – Rob
    Commented May 26, 2022 at 13:40
  • 8
    Even washing latex paint off of brushes can kill off that bacteria - it's pretty sensitive stuff.
    – user82600
    Commented May 26, 2022 at 16:30
  • 3
    I think that latex paint includes a variety of bactericides and fungicides to inhibit growth in the tin.
    – D Duck
    Commented May 26, 2022 at 18:14
  • 2
    Nope. It's added to inhibit growth on the paint film after application. I've worked in the coatings industry for 21 years. We even add more mildewcide to the paint upon request.
    – Rob West
    Commented May 27, 2022 at 20:49

If you search for "toilet tablets" you'll find a range of products designed for this purpose, with tank cleaning as a side effect of cleaning the bowl.

Many of these products include bleach, like the Clorox brand.

These have been around for many years and toilet manufacturers are well aware of them. You'll hear about how bleach can damage the rubber flap in the tank or the plastic parts in the fill valve, but manufacturers have replacement parts that aren't affected by bleach. If you have an older toilet, you might eventually have to replace these parts because of bleach, but it's also likely that you need to replace these parts anyway simply because of age. They are user replaceable parts for a reason.

Toilet tabs are a safer and longer term solution to a single application of bleach. With the tabs, you can cut the packaging and drop in the tablet without touching it or risking spilling anything. With bleach and a measuring cup, there's a much greater chance of spilling. And with the tablet, it stays in the tank until it's eventually used up, where the bleach is 1 and done. The tablet is also safe enough for normal use, while straight bleach may still cause burns or a reaction on "sensitive parts" even when diluted.

I've used a variety of these tablets for probably a decade or more and haven't had a problem. I tend to go with the ones with bleach and don't color the water. I've only had to change 1-2 flappers in all that time, and they are inexpensive. They are really easy to replace, too. I've also only had to replace 1 fill valve, and that was obviously old before I ever put in a bleach tablet.

I have seen rubber seals on the bolts holding the tank onto the body of the toilet dissolve into the water and crack, but again, that was due to age of the toilet. Those are fairly easy to replace and also have bleach resistant options.

  • 3
    The two times I’ve tried these things the rubber in my tank went to shit, pardon the pun
    – Taekahn
    Commented May 29, 2022 at 2:23
  • @Taekahn, not all rubber gaskets are good quality or designed to handle bleach. That's why I mentioned the ones that are. I've had gaskets that warped and dissolved without using bleach, so there's all kinds out there. Commented May 30, 2022 at 18:41
  • Yea, but how are you supposed to tell which ones will be affected and which wouldn't????
    – Brad
    Commented Jun 15, 2022 at 1:59
  • @Brad, they usually say so right on the packaging, since it's a sales point. For example: homedepot.com/p/… Commented Jun 15, 2022 at 14:48
  1. It's okay to, but people talk about an infrequent "shot" of bleach. Using things like dissolving tablets of bleach, or anything that lives long-term - the chlorine will have a bad affect on plastic and rubber parts on the toilet tank, and make them fail quicker.

  2. Much of the "scum" you complain about isn't actually organic alge/bacteria - but are other things in the water from rust, minerals, or any other types of weird non-soluble particulate matter - which when allowed to settle over years and decades of stagnant water in your bowl will accumulate. Bleach (or anything else meant to "kill stuff" won't help with this).

A better solution might be to put a little bit of soap in the back of the tank, and scrub it a bit with a (long-handled) brush maybe once a year. One thing that I've personally discovered - is that some of the stuff that accumulates isn't even aqueous - i.e. it doesn't dissolve in water at all. So this type of mechanical agitation is probably the only thing that would help with that.


While this is ok to do (as others have said), don't be surprised if this doesn't solve the problem. That "scum" look you're seeing may not be mold or bacteria at all, but mineral deposits that bleach won't do much about. If the bleach doesn't do anything, you may be left scrubbing after all.


While some bathroom cleaners contain bleach i.e. hypochlorite, it's actually the disinfecting property of that oxidant and not so much the destaining action that is of interest in this application. As others have already pointed out, many stains around water plumbings and tanks are minerals, limescale, metal oxides, green, black, brown rusty crusts. To dissolve these deposits many bathroom cleaners contain acids. Cleaners containing sulfamic_acid work pretty well for that. The true DIY solution, and more eco friendly, would be a mixture of citric acid and ascorbic acid, yes vitamin C as an additional reducing agent. Dissolve some spoons full in hand warm water and try that. Bleach is fine, if it is actually mold. But never mix bleach with acids! Try them in two different steps.


You can get septic tank type draino it adds bacteria back to the tank too. Yes the flora in the tank is vital to the function of the tank the layer of bacteria floating on top makes sure everything settles to the bottom you add bacteria frequently to make sure it does any bleach would be bad.

Yeah I add bleach to the tank a lot in the same way you add chlorine (bleach) to keep a poool clean

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