What are the best cleaning agents for carbon residues on glassware?

Introduction
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Recenly I wanted to isolate some ascorbic acid (Vitamin C or chemically - $\ce{C6H8O6}$). I've put the filtered solution (I had to filter it because of the binder) in a flask and heated it. It didn't go as planned because then I didn't know that ascorbic acid decomposes at high temperatures, but I still decided to keep the product of the reaction. I left it on a hotplate at a high temperature and it all went back to carbon because it was there for too long (It was dehydrated). 




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The cleaning agent that I know of - $\ce{NaOH}$
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I used a saturated solution of $\ce{NaOH}$ to clean it but there were still some flakes stuck on the wall that I couldn't reach. 


It worked well for me - cleaned ~90% of the residue. 




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The question
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**Are there any other cleaning agent that'll work better than aqeous Sodium Hydroxide?**





> 
> Are there any other cleaning agent that'll work better than aqeous sodium hydroxide?
> 
> 
> 


Yes, but **I would not recommend them to anybody running experiments at home!**


Back in the days in the lab we used arm-deep tanks filled with a saturated solution of potassium hydroxide in isopropanol to soak dirty flasks. You need long (!) chemical-resistant gloves and once in a while, the whole mess has to be discarded and replaced. Down the sink is not an option ;-)


And there is *piranha solution*, a mixture of 30% hydrogen peroxide and concentrated sulfuric acid. While is is effective, it is infamous for going off with a bang, see this [report](http://cenblog.org/the-safety-zone/2015/1/piranha-solution-explosions/).


To sum it up: Stay with the sodium hydroxide solution. Don't risk your health and don't screw up your own environment to rescue a spoiled flask.


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