Avon: The bass could all be done on an a standard 4-string tuned conventionally, he's even playing a lot on the D & G string several frets up the fingerboard, so not even low for standard tuning.
No One Knows: drop down to C, but as I said it's only harmonics of the full timbre you're hearing, not the fundamental low C (33Hz!). You're basically only hearing the "twang" of a note that low, albeit a growly twang, like a child trying to sing a low note; none of the thump. He often rises up from that low pitch when emphasis in the bass is needed.