A system for mixing paint and for holding a container of paint having a cover engaging a body is disclosed. The system comprises a rotary mixer comprising a holder configured for receiving the container. The system also comprises a clamp comprising an arm configured to pivot from a first position to a second position and a plate configured for positioning between a first linear position and a second linear position. The plate in the second linear position maintains the engagement of the cover of the container to the body by compression to inhibit leakage of the paint. A method of mixing paint with a rotary mixer is also disclosed.