I was able to remove the annoying yellowing effect from old white and lightgray bricks with the usage of hydrogen peroxide. With great results I have to say. Now I wonder what to do with the remaining fluid. Is there a danger to poison someone when it's used in my household? Is it ok to drain it down the sink? Any advice on how to deal with it is welcome.

Another thing, when do I have to change the fluid? Will the effect gradually decrease?

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    I'm voting to close this question as off-topic because the handling of H2O2 is not tied to LEGO bricks in any specific way. This question seems better suited to Chemistry.SE
    – zovits
    Commented Feb 20, 2019 at 11:37
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    The dangers of H2O2 depend greatly on the concentration, which, in turn, will quickly change with time as it decomposes to water (heat and light speed up the process). So small amounts of diluted H2O2 can be poured down the drain, by the time it reaches the main sewer, there will be nothing left that would be more problematic than the average household cleaning products that get down there daily.
    – zovits
    Commented Feb 20, 2019 at 11:42
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    Interesting point. I would say it fits in both forums. And considering the special relationship of the members of this forum to the brick in particular I would say that there is a general interest here for the topic. So, no, I would not change.
    – fabian
    Commented Feb 20, 2019 at 11:43
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    You have a point, I'll let the other members have a say in how strictly are the rules to be interpreted. Meanwhile, to see if an amount of H2O2 is still potent, one just has to watch for bubbles of O2 being generated inside the liquid from the spontaneous decomposition. No new bubbles means no more potency, and thus time for a change.
    – zovits
    Commented Feb 20, 2019 at 11:50
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    ahh, seems i have to change. Thank you Zovits for your fast help
    – fabian
    Commented Feb 20, 2019 at 12:02

1 Answer 1


After doing a simple search, it seems that the general consensus is, it's okay to pour the used amount down the drain.

Most of us get it. The stuff's been sitting in your house taking up space, and because of the unfamiliarity with this chemical, you and environmentally conscious thinkers such as yourself, would never want to further harm our shared environment.

Bottom line: No new bubbles means no more potency, the green light to pour away.

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