This is the toilet tank in my apartment. A few days ago I started noticing brown residue in the water. Upon investigation, I encountered a toilet tank I'm not familiar with... there's an "outer" tank, which is the one that fills with water, and a smaller, inner tank, which gets its water supply from the outer tank and is where, from what I can gather, the toilet actually flushes.

However, as you see from the pictures, while the inner tank is clean, because it always empties upon flushing, the outer tank only empties about halfway through, and the algae keeps accumulating and never reaching the bottom.

I've poured some bleach and started using those pills, but I'm not really familiar with this kind of toilet. Is it normal for the outer tank to not flush all the way down? It seems like a very strange and counterproductive design to me... the little white tank has "patent pending" written on it.

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update: Looks like this is the toilet model http://youtu.be/2SzVAwPAuJ0

  • Does the tank refill to above the lip of the inner tank? Does the inner tank look like an addition to the outer tank?
    – DJohnM
    Jul 24, 2014 at 0:15
  • That is a pressure assisted toilet. I've never owned or worked with one, so I'm not sure exactly how low the water level should be expected to go (thus not an answer). Some Google searches might turn something up now that you know what it is.
    – Comintern
    Jul 24, 2014 at 0:21
  • @User58220 the water refills slightly above. maybe a cm. looks like not an addition. hm, found this looking for "bsb" toilet youtu.be/2SzVAwPAuJ0
    – o_o_o--
    Jul 24, 2014 at 0:47
  • Looks like you have this: watermatrix.com/proficiency/pdf/Proficiency_UHET_english.pdf Not a normal design; it's using much less water than even most low flow toilets.
    – Zhentar
    Jul 24, 2014 at 15:09

1 Answer 1


I suspect the water level is set too high, so it's not emptying fully. I'd try adjusting the fluidmaster fill valve (the black thing on the left)

Here is a link to a troubleshooting guide for that toilet, check the poor or sluggish flush sections.


Those fluidmaster fill valves are cheap and it may have been replaced once already and not been adjusted the same as the original.

It may also have been that the toilet sat unused for a while allowing the algae to grow and just killing it off once by scrubbing the toilet clean will prevent it from growing back with normal toilet usage.

Using bleach and tablets in the tank is generally not a great idea because the chlorine breaks down the pvc used in the plastic parts. I know the fluidmaster parts always have a warning against it and the guide for your toilet also mentions not to use them.

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