Abstract: Condensate discharge line treatment to keep the line open, or to clear it if clogged. A valve is inserted into the discharge line and provided with an alternative inlet to receive flushing liquid. The valve inlet from the upstream part of the condensate discharge line is blocked by a valve member from time to time in favor of flow of the flushing liquid via the alternative inlet into the valve and out through the outlet into the downstream part of the condensate discharge line. The flushing liquid may contain a cleaning composition or even an algicide, which may be injected by manually or mechanically squeezing a flexible container of it to inject it into the flow of flushing liquid.