Duck tape is perfectly correct, it was the original name given to the tape with it only being used for duct work much later on.

From The Wikipedia article:

“Duck tape” is recorded in the Oxford English Dictionary as having been in use since 1899[2] and “duct tape” (described as “perhaps an alteration of earlier duck tape”) since 1965.[3]

It was originally used for making shoes stronger and was later used for sealing ammo tins.