A drain valve including: a support portion having a first end and a second end, the first end having a width that is narrower than a width of the second end; a connecting portion extending from the support portion proximate the first end, the connecting portion comprising a tip disposed at a proximal end of the connecting portion, the tip being configured to engage a drain defined by a panel; and a contoured flap extending from a hinge disposed proximate the first end from a flat lateral surface of the support portion, the contoured flap having a profile corresponding to profile of the portion of the panel and having a durometer value that: allows the contoured flap to pivot on the hinge to allow flow from the drain; and in response to a negative pressure within the drain, allows the contoured flap to prevent flow through the drain.