Hit the bottom of the barrel

• Went down in the ocean
• Went like the Titanic
• Sent to the ocean floor
• "Sighted sub, ___ same."
• Went down like a cement block
• Sent to the bottom
• Dropped sharply
• Submerged
• Dropped, as spirits

The Collaborative International Dictionary Word definitions in The Collaborative International Dictionary
Sink \Sink\ (s[i^ ng]k), v. i. [imp. Sunk (s[u^ ng]k), or ( Sank (s[a^ ng]k)); p. p. Sunk (obs. Sunken , -- now used as adj.); p. pr. & vb. n. Sinking .] [OE. sinken, AS. sincan; akin to D. zinken, OS. sincan, G. sinken, Icel. s["o]kkva, Dan. synke, Sw. ...