ues Sotah 29 (but I'll write on the end of 28)

Since we compare Safeik Tumah to Sotah, we're only stringent in Reshus haYachid.

Tosfos brings an argument if someone touches a Sheretz at night and in morning he finds that it is dead, R' Meir says he's Tahor. The Rabanan say that he's Tamia. Since we find it it dead, we can assume that was its status the whole night (Since we never established it to be alive.) However, they agree if you established that in the beginning of the night it was alive, then he's Thor.

Tosfos concludes that they says he's Tahor because tehy consider this to be a Safeik Tumah in Reshus Harabim. Tofos asks: this doesn't it well in the Mishna in Taharos that say that nighttime where all is dark, even in the streets where all is open, has a status of Safeik Tumah in Rushus Hayachid. This is confirmed by the Yerushalmi that says that a woman becomes a Sotah even in a street at night.