For next time you remove the intake manifold or a cylinder head, first pump out the water from the engine water jackets using a windshield washer pump and some windshield washer hose.
remove the heater hose from the manifold and stick the WWpump hose down the heater hose nipple. it will go down into the cylinder head water jacket. Pump it into a bucket or jug.
Pump out enough water/coolant to get the level below the level of the decks of the block.
Now you won't spill water/coolant down in the oil pan when removing the heads.