A spirit prayer pig is a prayer-restoring familiar that can be created in the machine under Eli's farm, after completion of the Bringing Home the Bacon quest. The familiar comes in three tiers. Each tier increases the usefulness of the pouch. To increase the tier of the pigs, one must upgrade the machine in the storm cellar. Each tier uses the same pouch. Upgrading the machine after obtaining a pouch still summons the higher-tiered familiar.
Prayer pigs have a right-click option "Restore prayer", which restores some of the player's prayer points from those stored in the pig. The pig starts out with a certain number of points, depending on the tier. Once the points are drained, it will regenerate points every 120 seconds until it reaches its initial points again. For the tier 3 pig, the maximum prayer points that can be restored will be 840 + 27 * 210 = 6510.