'A thing of' is a very Irish way of describing an inanimate object, usually a container or packaging of sorts. Be it down to laziness, or actually not knowing the name of what the object is, this expression has many uses.
Euphemism describing the act of defecating, metaphorically speaking. Otherwise known as taking a good hard shyte for oneself. This particular expression is used when the excrement is of a particularly large and solid nature.