When I hear people say "plumbing" it seems to mean not data conversion but the internal workings of a system, especially anything infrastructurey. So "meat grinding" seems more specific. But I like it because it's appropriately disdainful. Who wants to grind meat all day?

Dostoevsky said that if you want to drive a man insane all you need to do is sentence him to hard labor moving a pile of dirt from one side of a prison yard to another – and then back again.

Fitting data in whatever form it has taken at point X in a program into the form that API Y expects is often more like meat ungrinding.