Diagnosis
For the Ninja Kitchen System TB401, leakage from the bottom during blending is almost exclusively caused by a compromised seal at the blade assembly. The primary culprit is the black silicone gasket (O-ring) seated in the lid of the 6-blade assembly. Over time, this gasket can become cracked, warped, stretched, or can develop food particle buildup that prevents a tight seal.
How to Fix It
To resolve the leak, focus on the blade assembly. First, unscrew the blade assembly from the bottom of the 72-oz pitcher. Inspect the black silicone gasket inside the plastic lid piece. Remove it completely and check for any tears, nicks, or permanent deformation. Clean both the gasket and its groove thoroughly to remove any residue. Ensure the gasket is reinstalled snugly into its groove—it should not be twisted or folded. Finally, screw the blade assembly back onto the pitcher by hand until it is firmly tight. Do not use tools, as overtightening can crack the plastic and cause new leaks.
If That Didn't Work
If the gasket looks fine and is properly seated, inspect the pitcher itself. Look for hairline cracks, especially around the threaded area where the blade assembly screws on. Also, check that the clear plastic drive socket on the bottom of the blade assembly is not cracked and that the metal blades spin freely without wobble. If you find any damage to the pitcher or blade assembly housing, you'll need to replace the specific damaged component.
Heads Up
Always ensure the pitcher and blade assembly are completely dry before assembling. A wet gasket or threads can slip, preventing a proper seal. Also, blend frozen ingredients in pulses to avoid excessive strain on the seal from thick mixtures.