Just found a new method.
Worked for me.
My water fall sound form the Heater core is GONE.

1) unsnap the coolant tank and raise it.
2) get a screw driver. Have the screw driver hold the coolant tank on to the plastic cover of the battery. Goal is very high up coolant tank.
3) Remove the cap of the coolant tank. Coolant may spew out if you have air pressure trapped in the system.
4) Fill the Coolant to the cold line.
5) Put an allen wrench under the throttle stop to open the throttle to have the engine run at 2,300 RPM or so.
6) wait about 20 minutes to 1/2 hour. If the coolant spews out when revving the engine to 2,300 RPM, then you have other problems - like a bad head gasket.
7) The coolant level should have lowered as the air is now purged.
8) add more coolant to the cold line.
9) replace the cap on the coolant tank.
10) remove the allen wrench.
11) Turn off engine.
12) Put coolant tank down into it's area snapping it into place.
13) Drive some and listen for water fall sound. Heater on HOT/Max with fan on LOWest

If all is well - the water fall sound will be gone.

If the sound is still there - you may have an air leak in the cooling system.
Check all hose clamps.

Or, may be a head gasket.
Once I replaced the head gasket on my Discovery II, all this spewing out
coolant was done and over even when revving the engine with the coolant cap off when it is hot.

 

Seriously
put the bottle as high ad you can
wedge it do it stays there
take the cap off it

engine
start and hold at 2000 RPM
for 25 minutes

coolant level will drop as air comes out

then
turn off engine
add coolant to a bit below the cold line

put the cap on

put the bottle back

you are done

this worked for me

forget the valve at the T connection
don't use it

can actually let air in
if your coolant level in the bottle is low
and the bottle is not raised