1. To pull the chain on an old fashioned elevated toilet tank in order to flush fecal matter from the commode.
2. Flushing something down the toilet so that it ends up in the septic tank.
3. When a prototype ship model design fails hydrodynamic testing in a water-filled tank.
4. Naval aviators who fail to pass the dunker (Helicopter Underwater Escape Training) which is conducted in a large water tank.
My grades are really tanking this semester.
During testing the new ship design tanked straight away.
Ensign Smith just tanked the HUET test.
Verb: To "tank", or "tanking", would be the action of performing the duties of the tank as described above.
2.V. The warrior is tanking the mob right now.
3.V. Do you think you can tank this mob for us?