GreyWater is all the dirty water from your dish washer, shower, washing and bath. All this will go into your septic tank, so try not to use to much anti bacteria or bleach as this could kill the friendly bacteria.
Blackwater is the water you flush down the toilet and into the septic tank, again try not to use too much bleach or toilet cleaner.
Rainwater is water that is collected by the roof guttering that drains into your septic tank.
Remember all this waste water enters your septic tank. A yearly septic tank emptying service is advised.