Take a deep breath in, hold it for a moment, now exhale, notice the relaxation the softening, the relinquishing of the breath!
Personally I would say they can be combined in every moment of grasping, not just one session for one 'focus'. one sees the uncertainty of something being a stable foundation for happiness so is unsatisfactory, dispassion arises and so does the cessation of its allure.
breathing in focusing upon relinquishment is seeing that something is needed yet not satisfactory, so no passion rises for it. like with food, breathing, or even friendship.
He who knows only his own side of the case knows little of that. His reasons may be good, and no one may have been able to refute them.
But if he is equally unable to refute the reasons on the opposite side, if he does not so much as know what they are, he has no ground for preferring either opinion …
He must be able to hear them from persons who actually believe them … he must know them in their most plausible and persuasive form.