Thanks to Michael Quinion’s admirable newsletter on word history (link), we learn that there really was a Mr. Bowser:
Floods have caused enormous damage in parts of southern
We owe its existence to the late Mr Sylvanus Bowser, of Fort Wayne, Indiana. Early in the twentieth century he invented what he called the self-measuring gasoline storage pump but which we have long since abbreviated to petrol pump or gasoline pump. ... At some point, the usage extended beyond providing fuels to supplying water, especially in military situations and on construction and building sites. They may not have recognised the word, but many flood-affected people have been very grateful for bowsers.
Fn.: Cleaned up to ungarble a garbled paragraph, January 20, 2008.