An embodiment of the disclosure is a rack adapted to engage a rack handler. The rack includes a rack body. The rack body has a bottom, a top opposite the bottom, and a receptacle that extends from the top toward the bottom. The receptacle is sized to receive the sample collection unit. The rack body has a first interior surface that extends from the bottom toward the top, and a second interior surface that extends from the bottom toward the top. The second interior surface is opposite to the first interior surface so as to at least partially define a slot along the bottom. The rack body also includes an interference groove in the slot along at least one of the first interior surface and the second interior surface. The slot and the interference groove are sized to engage a portion of the rack handler.