Rapp Scallion took it with him to his grave having swallowed it for safe keeping.
Threepwood found Rapp's coffin inside a crypt by reading a book called Famous Pirate Quotations and matching his quote to his coffin. Inside it however was no map, but just the ashen remains of the pirate.
In the Voodoo Ladys shack, Threepwood found a potion that could resurrect the dead. He asked her about it and she told him that he would need a sample of ashes from the deceased whom he wished to revive and a recipe book called The Joy of Hex because she was not completely sure of how to construct it.
After delivering the ashes and the book to the Voodoo Lady, she prepared the mixture for him and let him take it to be used.
Threepwood used the Ash-2-Life potion to resurrect Rapp and ask him about the map. He said he would take that secret to his grave, but Threepwood reminded him that he had already done that, so Rapp agreed to trade the map for a favour. He felt that his soul could not be at peace until he was certain that the gas in his Steamin' Weenie Hut had been turned off. He asked Threepwood to check it and gave him his key in order to do so.
Threepwood went to check the gas and it was indeed on, so he switched it off before returning to Rapp to let him know it was done.
Rapp Scallion regurgitated and gave Threepwood the map piece before laying to rest for eternity.