Minions manaFollow

If your specced Demonology and have the mana feed talent you can lifetap and it gives mana to your pet.

if your afflic then you should be using your imp for leveling. atleast for me every time my imp ran out of mana i did a pit stop and his runing out of mana was pretty rare, dont forget that you have life tap, don't rely on dark pact for everything because if your going to respec later on it will be a hard transition at least it was a little for me

Other than mana feed, there's nothing to actively restore your minion's mana. Things to watch for, however, are making sure that your pet gets buffed when possible for more mana (pally: Blessing of Wisdom, disc priest: Divine Spirit). Also, turn off her other abilities if you need to conserve succy mana for seduce. Lash of pain isn't necessary for the time you send her in to dps once the group picks up your target... just let her auto-attack.