Translation:In the evening you fill the dirty tub.
A "labrum" in anatomy is more generally a structure with the shape of a kind of lip, a edge or brim.
As the firt meaning for "labrum" is "lip", not "tub".
I have no idea why it was first "lip" and then "basin".
Edit: I've found the explanation.
It's not the same word! Homonyms.
1/ Labrum from lambere (to lick) = lip.
2/ Labrum from lavare (to wash) = basin to wash someone/something.
Derived from lavābrum (“bathing tub”), from lavō (“to wash, bathe”) + -brum.