What type of bass clef is used for the organ pedals: regular bass clef, or 8va bassa?
Use the regular clef. The lowest written note is C two leger lines below the staff. The highest on a modern instruments is G three lines above the staff, but on older instruments the pedals may stop at F, or even D.
The sounding pitch of notes played on the pedals can be anything from two octaves below (or even three on a very few instruments) to two octaves above the written pitch. For example, in 18th century church music the pedals sometimes play "the tune" at the pitch of the treble part, not the bass line.
The "default" sound is an octave below the written notes.