A drainage device and a method for draining a liner-type medical suction apparatus and a rigid-walled container. The drainage device preferably includes a swingarm, a drainhead, and a suction source. The drainhead is positioned to be in fluid communication with the liner-type suction canister or the rigid-walled canister. The swingarm rotates to activate the suction source and inverts the liner-type suction canister or rigid-walled canister. The contents of the canister drain to a sewer system. The method includes the acts of placing the canister on the drainage device, coupling the drainhead to the canister, and activating the suction source.