On the other hand, I'm not sure it is so clear that {tlhagh} is the object of {'Im}.  KGT says, "the general word for "boil" is {pub}, but the verb used specifically to refer to the boiling of fat is {'Im} ["render"]."  However, I believe the only example we have of {pub} uses the thing being boiled as the subject ({pubtaHbogh ghargh HIq} from CK).  Does {'Im} work like {pub} and the thing that is rendering should be the subject?

No, it's not completely clear whether 'Im tlhagh or tlhagh 'Im, or both, are correct. (Even with an example of the subject of pub being the thing boiled, it's not certain that you can't pub something. Sometimes Klingon verbs go both ways. We actually have another example: tujpa' qul pub SuvwI' 'Iw a warrior's blood boils before the fire is hot.) I don't think the contrast of pub and 'Im in the text necessarily implies similarity in their transitivities.

When we lack an example, we have to go by the English translation. 'Im is render, boil fat. Now, it could just be saying that 'Im is the type of boiling that happens to fat, but the English translation does choose to use fat as its object. This puts me in favor of tlhagh 'Im. But if I saw 'Im tlhagh, I'd understand where you're coming from. If I saw 'ImwI' I'd be less comfortable, because I'd be imagining the cook doing the rendering, rather than the fat being rendered.

Let me know when you figure out which way to interpret tlhe'...

-- 
SuStel
http://trimboli.name