His Baseball Reference major league page is a good example of why I do this blog. The list of transactions end with his being purchased by Washington in 1947, though his career continued into the high minors afterwards...leaving open the question "How did he get to Seattle from the Senators?"
He could have been released by Washington, or traded for another player. It turns out, according to this article from the Milwaukee Journal of Dec. 29, 1949, his contract was sold to the independent Rainiers...
“The Washington Nationals Wednesday sold infielder Mark Christman, 36, to Seattle of the Pacific Coast League for Cash, Vice-President Calvin Griffith announced.”
As a baseball nut, I think that is important to note. Christman didn't last long in Seattle, and was given a chance to go to Milwaukee. From the Milwaukee Journal of June 5, 1949:
“Mark Christman, former major league infielder, is going to join the Milwaukee Brewers, President Jake Flowers announced Monday. Christman, who was given his free agency by the Seattle club of the Pacific Coast league last week, accepted term in a long distance telephone conversation.”
Christman played for a couple of lower minor league clubs as he went into coaching.