How long does heroin show up on a mouth swab?

yes. It will most likely show up as Morphine depending on how long it has been since you have used. Because that is what your body metabolises it into.

3 days

K2 will only show up on a mouth swab test if you use it 12 hours or less prior to the test

if marijuana does then pills will too, you should be alright if there was some time from the last time you used to the drug test, but if not you're probably screwed, try dipping or smoking...

36 hrs