Empty the Jordan: a Scholarly Enquiry

In Act II, Scene 4 of Shakespeare's Henry IV Part II, at the Boar's Head Tavern in Eastcheap, Falstaff enters:

[Singing] 'When Arthur first in court,'

And then says:

--Empty the jordan.

Jordan?  The online dictionary gives:

n:   1350–1400;  ME jurdan  urinal, perh. after Jordan,  the river, by coarse jesting.

 In last week's London Globe performance--the nearest  I have ever see, I  suspect, to a Shakespearean original, Shakespeare precedes his mandate and his song with a 45-second episode of epic disencumbrance.  It is all in the best of taste, done from under a flowing blouse with no dangly parts on display. But there can be little doubt that the "jordan"--here a dun-colored clay pot--is well and truly filled.  Fallstaff's  boy dutifully executes his master's command; he attempts first to dump it all back into the wine cask, but Mistress Quickly administers a hearty smack and he scampers offstage.

But here's the thing: the command is right there in the Shakespearean script.  The stage business which precedes it is nowhere to be seen.  Which inspires the question--really, two questions:

• Who was the first Shakespearean scholar, director or dramaturge who first grasped that a jordan, in order to be emptied, must once have been full; or

• Can we assume that this bit of merriment goes right back to the 1590s?