A drill bit assembly for boring including a drill bit and a bit sub. A front bit end has a plurality cutting elements at a forward face of the front bit end and a first fluid return passage extending through the drill bit to a rear bit end. The bit sub couples to the rear bit end. The bit sub includes a bore disposed at a front sub end sized and shaped to receive the rear bit end of the drill bit. A plurality of legs extends from a mid-sub region toward the front sub end between pairs of cutting elements. The plurality of legs has a fluid delivery passage disposed therein with the fluid delivery passage extending from the plurality of legs to a rear sub bit end. The bit sub has a second fluid return passage connecting the first fluid return passage to the rear sub bit end.
