linarite,
in Germany potassium permanganate is readily available in all pharmacies/drugstores in crystalline form.
You will notice that the deeply purple coloured solution (you can achieve this by a very minor amount of potassium permanganate, just the tip of a knife should be enough) will turn into a brownish colour after half an hour or so. A few hours later it will be completely brown which means all the potassium permanganate has become inactive (=oxidized) and what's left over are essentially plant nutritients:
4 KMnO4 -> 4 MnO2 + 2 K2O + 3 O2
If you rinse the bamboo well, there will be no danger for anything in your tank. The potassium permanganate itself is an extremely strong oxidizing agent and will kill basically anything that lives in large enough amounts.
I would recommend to bath plants for only 5-15 minutes. I always treat my
new plants like that to get rid of any unwanted guests and never had any problems. You can leave the bamboo in the solution for as long as you like.
The inactive solution is safe to be just flushed away.
'I ought never to act except in such a way that I can also will that my maxim should become a universal law.'