I'll make an attempt at the first two: tattie wallah and Gunga Din.

According to the online version of the Merriam Webster a wallah is "a person who is associated with a particular work or who performs a specific duty or service -- usually used in combination (the book wallah was an itinerant peddler -- George Orwell)".

(The Hindi and Sanskrit terms it derives from give it connotations of "one in charge" and of "guarding", but that didn't carry over into the meaning of the English term.)

Wikipedia says, "Gunga Din is one of the more famous poems by Rudyard Kipling. Perhaps best known is its often-quoted last line, 'You're a better man than I am, Gunga Din!' The poem is a rhyming narrative from the point of view of a British soldier, about a native water-bearer who saves his life. Like several other Kipling poems, it celebrates the virtues of a non-European while retaining a colonialist view of such people as being of a 'lower order'." You can find the full text here at Bartleby's.

I cannot find any hint of what "tattie" is in this context. The only meaning I can find is the obvious: "tattie" = potato.

However, given the context of the song -- the wallah has water in his crown and is referred to as "Gunga Din", who in the poem was the regimental water-carrier -- I suspect that a tattie wallah is simply a water-carrier or water-seller.

BB,

NightWing