Including urine.
This precious liquid, so to speak, was used by tanners and dyers to treat their hides and cloths, and thus the tax on it proved quite lucrative. Still, it didn't stop many from complaining about it. Vespasian's own son, Titus, criticized him for this tax which he deemed absolutely ridiculous (I can only imagine how the tax collectors and auditors must have had their nostrils assaulted by the sharp smells).
But Vespasian was satisfied with his tax, and that is when people say he retorted that, "Money has no smell."
Interestingly, in the 19th century, some French (who wrongfully assumed then that Vespasian was the one who had created the Roman public toilets to help in his tax collections efforts) started calling their toilets Vespasiennes.
Source:
Roughly translated from a short article in the French magazine Les grandes figures de l'histoire No. 20.