ok well i have a tuner that tunes to drop tunings. it does this using a "flat" or "b" button. for example, if you wanted to tune to Eb you would press the button once or for low D you would press it twice, etc. Anyway, the max amount of flats it can go up to is 5. Seeing as four flats is what i use to tune the 6th string to C, and there is no Cb note, would i be correct to think that 5 flats is Drop B? Sometimes when i play it doesnt sound quite low enough though...im very confused.
You are correct.
Yes because Cb = B
yup dropping down a half step or a "b" from C is B