Tohoros 4:8-9
The rest of the chapter analyzes mishna 4:7 piece by piece.
Tohoros 4:8
“A doubt regarding something unclean floating on the water” is clean regardless of whether the water was in vessels or on the ground. Rabbi Shimon says that if it was in vessels, one is ruled unclean but if it was on the ground, he is ruled clean. Rabbi Yehuda says that if the doubt arose when a person went down into the water, he is ruled unclean but if it arose when he was coming up from the water, he is ruled clean. Rabbi Yosi says that even if there is only enough room in the water for a person and the ritual impurity, the person is ruled clean.
Tohoros 4:9
“A doubt regarding whether liquids were rendered unclean is ruled unclean” – If a ritually-unclean person extended his foot between ritually-clean liquids and there is a doubt as to whether or not he touched them, the case of doubt is ruled unclean. If he had an unclean loaf and he threw it among clean liquids and there’s a doubt as to whether or not it touched them, the case of doubt is ruled unclean. “But a doubt regarding whether they conveyed impurity is ruled clean” – Let’s say that a person had a stick, on the end of which there was a ritually-unclean liquid. If he threw the stick among ritually-clean loaves and there’s a doubt as to whether or not it touched them, the case of doubt is ruled clean.