Reference for Berakhot 49:12

א"ר פפא פי חזיר כצואה עוברת דמי פשיטא לא צריכא אע"ג דסליק מנהרא

Rab Pappa said : A pig's snout is to be regarded as passing manure [for the purpose of reading the Shema']. That is obvious! No; it is necessary [to mention it], because even if it just came up out of the river [it is to be so considered].

Jastrow