Submersion of the sink at night, or just before first light, to avoid disqualifying its contents: Zevachim 20a, 21a-b
When the kohen who would collect the ashes raised or submerged the sink for washing, that signaled the other kohanim that the time for washing had arrived: Zevachim 21b
Use of water from the sink to wash the meat of a korban olah: Zevachim 22a-b