Effect + Mana to mana pool

[Das_hessian]

If a card states " as an additional cost to sacrifice a creature and add 3 mountain to your mana pool" does the additional manna stay In my pool or does it go away after my turn is over?? Example: INFERNAL PLUNGE

[Nfidel2k]

106.4. When an effect produces mana, that mana goes into a player's mana pool. From there, it can be used to pay costs immediately, or it can stay in the player's mana pool. Each player's mana pool empties at the end of each step and phase.
106.4a If a player passes priority (see rule 116) while there is mana in his or her mana pool, that player announces what mana is there. If any mana remains in a player's mana pool after he or she spends mana to pay a cost, that player announces what mana is still there.

It goes away at the start of your next phase/step.

[Remillo]

The key thing here is that when an effect states "Add [Mana] to your mana pool", you're not adding that Land.  This is a common mistake newer players make, brought on by the fact that basic lands only have their corresponding mana symbols in the text box.  What that giant red mana symbol means on your Basic Mountain is "{T}: Add {R} to your mana pool".  Activating this ability adds a single red mana to your mana pool, and like most mana, it will empty from your pool when you move to the next step or phase in the turn.  When you use a card like {Infernal Plunge} or {Dark Ritual}, you're not adding three Mountains or Swamps (respectively) to your mana pool, but rather three mana of that color, and like most mana, it will end up leaving your mana pool at some point.  It's just like mana produced by a creature like {Elvish Mystic}; you're not adding the land that produces that color, you're just generating extra mana that doesn't come from your lands.