I'd try removing drain trap first, if its a bottle type the base of it will just unscrew, before using any chemicals.
One-shot is good, however I had a large problem with the stuff when I tried it on a shower drain in the ensuite (very difficult o get to the trap).
Poured the one shot down the drain, it fizzes a bit then the accumulate water disappears. Run the shower for a few seconds - looks clear

.
So I get undressed and have a shower.
Get out an hear this dripping noise, WTF? Wrap towel around me and run downstairs - water cascading everywhere through the ceiling and down hallway light fitting AAAHHH!!

Grab mop & bucket and start furiously mopping whilst trying to keep towel about myself due to the glass external door (laminate floor so I know it will not appreciate getting wet from previous kitchen experiences). Water is still dripping down on my towel clad self. It starts to sting. It starts stinging more - oooowww. Must till have 'one-shot' in it. Run back up to get in the shower, errrr...NO, can't do that now - head for the bath and try to get 6' 2" 16st under the tap (its really, really smarting now). Quick wash off and back to the mopping. Then another tip to the bath.
Later investigations revealed a flexible pipe under the shower had actually been dissolved, thus the 'blockage' clearing. Had the consistency of a plastic milk carton (the rest of the drain piping was fine). The episode cost a new laminate floor (edges started to lift) and we sill have a slight bulge in the hallway ceiling where the plaster has sagged slightly. I'm also still not sure of the long term effects the acid soaking has had on flooring and supports upstairs.