Draining coolant

[95Achieva]

My 95 Achieva with the 3100 has what resembles a plastic tab/knob where the petcock on the radiator normally is. Last time I drained the coolant I just removed the hose because the plastic thingy seemed like it wouldnt unscrew or loosen. Any tips on whether this is meant to be loosened, unscrewed, or removed to drain the coolant? Any info would be appreciated...it's plastic and I'd like some advice before I try to force it.
Thanks

[robby1870]

Should just twist right off.

[v6h.o.]

you have to twist it to unlock the drain, Then Pull the drain to open it up.

[95Achieva]

Thanks...I'll give it a twist and pull.