I left the tub lid a little bit open. Don't remember why I did that. Of course, the bp goes missing when I check on him a few hours later. He was found nearby so I was lucky.
On the same topic about tubs, I learned active snakes are more likely to get out of tubs (Not sure about racks) no matter how many binder clips and such you use (With the exception of my king, who stayed in a tub for a few weeks without issues). Best to go for one of those tanks that come with locks.
Don't stick your hand into the bag to get your new snake.
There were a lot of 'noob' moments that I can't remember. I got lucky and learned quickly thanks to others' advice and help.