Potassium permanganate changes from pink to clear on reacting with urine

KMnO4 was used by the cleaners to clean the water tank in our building. For a day or two all the water in our and taps cisterns was pink. On using the toilet before flushing I noticed that the colour of the water changed from pink to colourless because of urine. I couldn't understand why this happened, kindly help out.




The chemical reaction is the sum of the two following half-equations, one due to urea $\ce{CO(NH2)2}$ and one to the pink permanganate ion $\ce{MnO4-}$ :
$$\ce{CO(NH2)2 + H2O -> CO2 + N2 + 6 H+ + 6 e-}$$
$$\ce{MnO4- + 8 H+ + 5 e- -> Mn^2+ + 4 H2O}$$
The total of these equations needs to engage $30$ electrons, which gives :
$$\ce{5 CO(NH2)2 + 6 MnO4- + 18 H+ -> \\ -> 6 Mn^2+ + 5 CO2 + 5 N2 + 19 H2O}$$


As you see, urea destroys permanganate ions in acidic solutions.
The final solution is colorless, because it contains $\ce{CO2}$ and $\ce{N2}$ which are colorless, and $\ce{Mn^2+}$ which is nearly colorless.


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