Usually I think of Willie the Whaler as a little old man, not a sex symbol, but I have to say, this image is kind of sexy... I'm not sure if it's because he looks like he's doing crunches or if it's the boots. Probably the boots.
I don't know why he's decided the only way to use a "bring 'em near" (is that really easier to say than "telescope?") is to set his knees up like a tripod. It's a mystery. The "green pennant" is not a mystery, but "straighten the Monongahela with our addlings" is the most obscure thing Willie has said yet.
Of all the Wiki definitions for Monongahela only these might possibly fit:
Monongahela (lungfish), a genus of fish
Monongahela River, a waterway
USS Monongahela, one of various ships of the United States Navy
It's a pretty safe bet Willie is not referring to an album by the Oak Ridge Boys.
But I can't say for sure if it's a river, a fish or a ship that Willie proposes to straighten with "our addlings." Fortunately the indispensable Routledge Dictionary of Historical Slang has a definition for addlings:
Pay accumulated on a voyage or during a commission’: nautical, esp. naval: late C.19–20. Bowen.
I will hazard a guess that "straighten the Monongahela" is an expression derived from the second Monongahela, a tanker during WWII that limped home during the war which means - what else - to get drunk, and Willie is proposing - highly uncharacteristically - to actually pay his way.