If I recall correctly, first I used to use di water, but later on I used a solution. Whatever protocol is used in biological labs to wash flasks and tubes, I pretty much followed that, I don't remember what washing solution I used, I recall it felt like soapy water. It's possible that latter might have been the problem.

I would expect that solution to be incredibly aggressive. Wouldn't be surprised if it was lye (which feels soapy because it turns the outer layers of your skin into soap).