Tonight I did something I have never done before. I ruined two sheets of 12x20 film in a jobo. I developed the film in the 20x24 print tube. Everything went fine until I popped the top. I use the foot pump to get the top off. I did everything like I normally do, except that I put the tube on a stool when filling it with air. The seat of the stool is a cane seat and has some spring to it.
I put my hands on the top of the tube to keep it from shooting upward. When the top shot off, I ended up pushing the top down into the tube sideways. The top scratched both sheets of film. The sheets are now residing in the circular file.
Live and learn.