I remember doing that for the first time on my fizzy when I were a lad. I read the warnings on the tin about not getting it on the skin. Mixed it up with water, blocked the head end of the pipe with DumDum and tipped it all in. After a few seconds the whole lot spewed out of the pipe, which I was holding. It was like a volcano, it went all over my arms, but I held on because I didn't have any caustic left.
I thought I was in real trouble, but I have to say it didn't hurt at all, either at the time or later.
Full performance was restored afterwards.....
