Destroy or dispose of (something) irretrievably:someone had deliberately deep-sixed evidence...
They never really wanted to offend their corporate contributors, and now that the elections are over, they've deep-sixed any action to stop this tax scam.
The government clearly had no use for the commission's 1979 report and deep-sixed it on arrival.
Robbins should have deep-sixed the sentimental scenes and given us more caricature.
Origin
1920s (as the deep six 'the grave'): perhaps from the custom of burial at sea at a depth of six fathoms.