A method of forming an integral drain for a heat exchanger is provided. The method includes forming a plurality of passage walls to define a plurality of passages with an additive manufacturing process, each of the passage walls having a non-linear portion. The method also includes integrally forming a drain wall with at least one of the passage walls with the additive manufacturing process to define a drain for each of the plurality of passages, the drain wall located proximate the non-linear portion of each of the plurality of passage walls.