Kobold is indeed an American company and yes they dropped the U as it seemed the septic tanks struggled with the concept of the letter u in some words. The u was used in the old English language and you can still see it used in some older documents normally in Land survey deeds and old ships names. it is tricky to find out about as they normally hide this kind of info in books.
Sorry, friend. No harm meant. Just taking the piss as the Ozzies say (hope I've got that right).