A New York City man is on a mission to flush the cremated remains of his lifelong friend — a plumber — down ballpark toilets around the country.

Tom McDonald tells The New York Times that it’s a fitting tribute for Roy Riegel.

The two baseball fans were childhood friends in Queens, not far from — wait for it — Flushing Meadows, where the Mets play.

Like baseball, this endeavor has rules. The game has to be in progress when McDonald sprinkles the ashes into the toilet from a little plastic bottle.

So far, he’s done the deed at 16 stadiums.

Riegel also was a music fan: In Cleveland, McDonald flushed ashes at both Progressive Field and the Rock & Roll Hall of Fame.

In Chicago, McDonald did his duty at a White Sox game, skipping Wrigley Field because the Cubs are longtime rivals of the Mets.