Hi… I changed the oil in my Forester (as usual) and decided to change the coolant… Been a very long time since it was changed… Long before I bought it… The car has 340,000 miles on it, but anyhow I drained the radiator and not even half a gallon came out, and it was a very dark green… How do I get the rest out? Thank you in advance
See if you can locate a drain plug on the engine block to drain the rest of the coolant.
If not, see if there’s enough room to install a flush kit on a heater core hose.
A garden hose is connected to the flushing tee and the cooling system is flushed out.
If this won’t work, then fill the radiator with water and bring it to shop so the cooling system can be flushed and refilled with fresh coolant.
Tester
What is cooling system capacity? 2 gal? 3 gal?
I think if you remove the lower radiator hose on this one, it will drain the block. Refilling it and getting the air out is trickier. I don’t know why this should work but the guys at the Subaru forum recommend that you jack the front end up as high as you can, disconnect the upper radiator hose at the radiator and fill the system by pouring new coolant into the upper radiator hose until it backfills the radiator from the bottom.
Be sure to go to the Subaru dealer and get some of that conditioner so you don’t blow your head gaskets.
I always just disconnect the lower radiator hose and drain it that way.
The lower radiator hose is next to the radiator petcock so there is no reason to disconnect the hose. Drain the coolant at operating temperature when the thermostat is open to allow the engine to drain. It is best to open the block drains but that requires more effort.
If you use the antiquated flushing tee you will have to drain the water from the engine before you can add the coolant.
For a flushing technique, does anyone ever use this?
- Open radiator petcock (or partially remove lower hose from radiator to get same effect).
- Remove radiator cap and put garden hose into opening. Turn water on full.
- Start engine. Let it heat up so thermostat opens.
- Keep garden hose volume high enough to keep radiator full or overflowing with water.
[Update]
5) Keep engine running and garden hose running till all entire system is flushed. i.e. heater is hot and water coming out radiator bottom is clean.
6) Shut off engine. Turn off garden hose.
Petcocks are too slow for my taste. I find it easier to just disconnect the hose. 
@JoeMario, I would be concerned about creating more hazardous waste and disposal with your method.
Our City has collection points and also say you can pour it into the sanitary sewer, not the storm sewer (the sewer system that collects rainwater in the streets)
I’ve used @JoeMario 's idea before, but I’ve always removed the thermostat and drained all the antifreeze that I could. I’d also pull the top radiator hose off and stick a pipe into it…then all the rust that comes out is pumped out the pipe and onto the ground.
I’ve done this to really do a good flush when the coolant has gotten so bad that it looked like it had snot floaters in it.
Yosemite
Since the thermostat is at the lower hose on this car, removing the lower hose will drain no more coolant than opening the radiator drain, unless you do it immediately after warming the car up to 200 degrees. That sounds fun, clean, and safe, doesn’t it?
You can remove the 90 degree bypass hose that’s to the rear and slightly above the lower radiator hose to drain some more coolant from the block. Be sure the system is bled of air pockets after you refill it.
@jtsanders and @Yosemite:
I agree. You do need to worry about environmental issues. It’s easy to capture the radiator drainage into a bucket. Capturing what’s in the block, without removing the block plugs, which are sometimes frozen, is another issue.
I don’t do that
You might try following this thread at a Subaru forum I visit. I got beat up pretty bad in this thread as you will see, but you might find it helpful.
The guys on that forum sound like a bunch of smug . . . fill in the blank
Just because they’re very familiar with Subarus does not necessarily make them any kind of car experts
Not to be too specific here . . . but at work one of our younger guys came from a dealership, where he exclusively worked on one brand for several years
He had a LOT to learn when he showed up. He’s a good guy, but it doesn’t change the fact that he was quite green in many respects
As did I, because I had been working exlusively on Benzes for many years
BTW . . . I like the way you stood up for yourself. 
A few methods posted of changing coolant which I have used in the past. I have a new method since I would now have to use those in my driveway. I go to dealer’s webpage. Schedule an appointment. Leave car in their hands. Walk across street to Denny’s and have breakfast. Walk back and retrieve car which has had coolant changed and replaced with proper coolant/water ratio with system pressure checked and old coolant disposed of conforming to EPA regulations. No muss. No fuss. I pay $60 and drive my hand washed car away.
I used to flush the cooling system your way @JoeMario . But I changed my method. Here’s how I do it now: starting with a cold engine I drain the radiator, then refill with water. Then I turn on the heater to max heat and run the engine until the thermostat opens and water circulates in the engine block and heater core, then turn the engine off and wait 20 minutes for the engine to cool off, then drain the radiator again. Repeat until what comes out of the radiator is clear, looking like plain water. It takes two or three times.
The reason I changed is I decided it might not be a good idea to pour cold water into the radiator when the engine is hot and running. The thermal stress of cold water hitting a hot engine part might damage something expensive.
This is my new procedure for coolant change. Access dealership website. Schedule coolant change. Deliver vehicle to dealership. Walk across street to Denny’s. Have breakfast. Walk back to dealership. Pay $60. Drive away in hand washed vehicle. No muss. No fuss. Proper coolant installed. EPA requirements met. No ill/dead pets/wildlife in my neighborhood.
+1 to @GeorgeSanJose
I use jugs of distilled water. I don’t understand using a garden hose with tap water if a significant part of that stays in the system when concentrated coolant is added.