That reduced diameter acts as a spring to absorb some of the torque being transmitted from the impact driver to the fastener.
The straight bit will not flex or elastically deform, but will fail in torsion without warning. These bits are not "impact rated", but are meant to be used with hand tools.
That looks like your floor drain.
The white pipe is the condensate drain from your A/C unit.
Where does that off-white/tan pipe go?
If I had to guess, the washing machine or sink drains into the same set of pipes.