The tube you see going up is the return line. I believe no check ball on it , oil wont run up there parked.
On mine at one time I had no oil pressure while on sidestand , but standing up it came back. Pulled a pump, checked it , and tried another pump I think..same thing., THIS is why I had the NOS pump all those years... bought it while trying to solve the oil pressure problem..
Then one day a guy, looked in the tank with a strong light, and saw the tube lying there. You could see it had broken off above the fitting end , INSIDE the tank... meaning if bike was not running, al, the oil went in the sump.
And when idling, there was not enough oil in the tank to fill the feed line, till you stood the bike up ... or revved it up and put oil back in the tank ..faster than it could run out. It was fine while running, pressure stayed up..
So Yeah, got a pretty good idea where the pipe goes to, and what its function is.
Many manufacturers just have tge line enter tank higher up, eliminates the problem.. Chopper guys like the clean look, all out the bottom.... only 2 lines on Amen .. clean looking..