On my 1998 model it was fairly simple. There is a drain bolt you loosen near the bottom, but be very careful as it's plastic and you don't want to strip the threads. Loosen it slowly and don't overtighten.
Draining is easy. Filling is more complicated. Here is an exchange from another forum:
Q: We don't have bleed openings on our Foresters either. What's the best way to get all the air out? Squeeze all the tubing a few times? Run very briefly and let it cool down; repeat many times? Other? A: I ran it about 5 miles then let it cool. Removed radiator cap and refilled. I repeated it a couple more times I believe. http://www.subaruforester.org/vbulletin/f88/engine-overheating-badly-wheres-ther- mostat-53935/#post601044
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Q: We don't have bleed openings on our Foresters either. What's the best way to get all the air out? Squeeze all the tubing a few times? Run very briefly and let it cool down; repeat many times? Other?
A: I ran it about 5 miles then let it cool. Removed radiator cap and refilled. I repeated it a couple more times I believe.
http://www.subaruforester.org/vbulletin/f88/engine-overheating-badly-wheres-ther- mostat-53935/#post601044