From: Rabbi Moshe Sofer
To: Rabbi David
The Chasam Sofer clarifies that hargashah followed by finding a tahor-colored fluid renders the woman tehorah, based on the Terumas HaDeshen's fuller formulation omitted by the Shulchan Aruch. He also disputes the Toras Shlomim, arguing that hargashah during pregnancy actually weakens the chazakah of siluk damim rather than being overridden by it, since a pregnant woman's mekor does not normally open, and uses competing chazakos to resolve the Beis Yosef's question on the Tur.
Source: Shu"t Chasam Sofer YD §168