I've never heard the chorus sung.
These are the lyrics I have, from the singing of Sean Oglesby, Dublin:

Saint Patrick Was A Gentleman    

Saint Patrick was a gentleman, he came from decent people
He built a church in Dublin town and on it put a steeple
His father was a Gallagher, his mother was a Grady
His aunt was an O'Shaughnessy and his uncle was a Brady

The Wicklow hills are very high and so's the hill of Howth, sir
But there's a hill much higher still, much higher than them both, sir
From the top of this high hill Saint Patrick preached a sermon
Drove the frogs into the bogs and banished all the vermin

There's not a mile in Eireann's isle where dirty vermin muster
But there he put his dear forefoot and murdered them in clusters
The frogs went plop, the toads went flop, slapdash into the water
The snakes committed suicide to save themselves from slaughter

Nine hundred thousand reptiles blue he charmed with sweet discourses
And dined on them at Killaloe in soups and second courses
Blind worms crawling on the grass disgusted all the nation
Down to hell with a holy spell he changed the situation

No wonder that them Irish lads should be so gay and frisky
Sure Saint Patrick taught them that as well as making whisky
No wonder that the saint himself should understand distilling
His mother had a shebeen shop in the town of Enniskillen

O was I but so fortunate as to be back in Munster
I'd rebound unto that ground and nevermore should want, sir
There Saint Patrick planted corn, cabbages and praties
He had pigs galore, a gra a stor, altar boys and ladies

Cheers,
Michael