Go down the tube/tubes
Definition 1 of 1
Pro Tip 1/3Figurative Meaning
Used metaphorically for situations that deteriorate, not just physical objects going inside a tube. 
His academic performance went down the tubes after he started playing video games.
Pro Tip 2/3Colloquial Usage
It's a casual phrase, more suitable for conversations than formal writing. 
I heard their project went down the tube - what a bummer!
Pro Tip 3/3Negative Connotation
The phrase implies a negative outcome and is often associated with disappointment. 
After the lead actor quit, the film production went down the tubes.