Activate Zuran Orb by sacrificing Drownyard Temple.
Each Scouring Swarm you control triggers, creating a tapped token copy of itself.
Resolve the Zuran Orb ability.
If you control four or more Scouring Swarms, activate Phyrexian Altar by sacrificing a Scouring Swarm, adding 1.
Repeat step 4 until you control three Scouring Swarms or until you have 3 available, whichever comes first.
Activate Drownyard Temple by paying 3, returning it from your graveyard to the battlefield.
Repeat.
This elegant loop uses Zuran Orb to feed Drownyard Temple into your graveyard, turning every sacrifice into fuel that Scouring Swarm needs to multiply its flying token copies once your graveyard is deep enough. With your swarm growing out of hand, you can then harvest the surplus creatures using Phyrexian Altar to generate the exact mana needed to recur Drownyard Temple back to the battlefield and start the cycle all over again.