From: Rabbi Moshe Sofer
To: Rabbi Yisrael
The Chasam Sofer rules that a copper spigot fitted at the base of a barrel-mikvah does not render the mikvah invalid, because the spigot does not qualify as a kli susceptible to tumah — it is neither a receptacle, ornament, nor independent functional vessel. Since tumah requires the legal status of a kli, the spigot is inherently tahor and the mikvah's waters are formed b'taharah.
Source: Shu"t Chasam Sofer YD §218