Thanks to Geoff for helping with the photography while I was busy inducing vomiting.
First you've got to get the tube in. It looks uncomfortable, but it beats getting cut open.
Flush with water, than lift by the tail. Then take the obligatory vomit shot.
Mmm... stomach contents... That's a spotted hake in the bucket and that nastily-bitten hunk of fish in my hand is a partially-digested tonguefish. Tonguefish are so far one of the few food items that have proven problematic with the stomach tube method.
Unless it's one of the few doomed to be sacrificed to measure the method efficiency (by comparing food lavaged out with food dissected out), this poor hung-over dogfish will swim away from this.