Why does the Torah see fit to specify "el Makom Tahor"?
Rashi: Because there is another place outside the town that is designated for Tum'ah - where they throw the stones of a house with Tzara'as 1 and for a Beis ha'Kevaros.
What is the definition of "mi'Chutz la'Machaneh"?
Rashi: Outside all three camps (the Machaneh Shechinah, the Machaneh Leviyah and the Machaneh Yisrael); and at the time of the Beis-ha'Mikdash, outside Yerushalayim.
Why does the Torah find it necessary to add "el Makom Tahor"?
Rashi: Because there was also a Tamei location outside the town that was designated for stones of a house with Tzara'as.
What does "el Shefech ha'Deshen" refer to?
Why does the Torah repeat "el Shefech ha'Deshen ... "?
Rashi: To teach the Kohen to burn the bull on that spot even if there are no ashes there. 1
See Sifsei Chachamim.
Why is it burned?
Moshav Zekenim (6): This hints that just like fire consumes everything, so "Machisi cha'Av Pesha'echa" (Yeshayah 44:22).
Why is it burned outside the camp, in public view?
Moshav Zekenim citing the Rosh: This is so one will not be ashamed [to confess] his sin, [rather,], he will confess on it, for [he sees that] even the Kohen Gadol confesses and brings his Chatas.