Abstract: A drain system is configured to collect condensate from flue gas generated by a condensing fuel-fired appliance. The drain system includes a drain body defining an inlet positioned to receive condensate in the drain body, a drain opening positioned to deliver condensate from the drain body, a passage extending between the inlet and the drain opening, and a seat surface disposed within the passage. A float moves within the passage of the drain body at a location between the inlet of the drain body and the seat surface of the drain body. The float moves to a position contacting the seat surface defined by the drain body to block the flow of flue gas through the passage of the drain body when there is little or no condensate in the passage. A neutralizing agent is positioned along the passage of the drain body for contact with condensate in the passage.