I don't know if there is one really.
there are allen screw plugs in the bottoms of both cylinder heads to drain
the block, but getting at them isn't easy or practical.
here's what I would do to get the most coolant out ...........
I assume this is a water boxer.
I'd undo the lowest main coolant hose I could find, remove the pressure
bottle cap, and catch all that coolant.
Then raise the front pretty high, and remove the bleed valve screw on top of
the radiator...........that should allow a lot of coolant to flow out of the
radiator, the main pipes, and the engine.

another strategy is to do it now, and since you'll never get more than about
75 % of all coolant out, counting both heater circuits too, do it again in a
month as well..........then you'll have changed about 90 % of it by the
second time.

I use conventional high quality  ( usually Prestone exteneded life in the
bright yellow gallon jug ) anti-frz mixed 50-50 with............ where I am
...........clean tap water, and I add 'water soluble oil'
............'cutting oil' that a machinist would use. Makes a wonderful
water pump lube and rust inhibitor - have been doing this on hundreds of
cars for a couple decades - works really well.
Scott
www.turbovans.com
----- Original Message -----
From: "Allan Streib" <streib@CS.INDIANA.EDU>
To: <vanagon@GERRY.VANAGON.COM>
Sent: Saturday, October 04, 2008 4:50 PM
Subject: draining coolant

> Before winter gets here, I want to drain and install new coolant in my
> Vanagon.  I've seen several posts about how to fill the system, but
> what's the easiest/most complete way to drain it?
>
> Allan
> --
> 1991 Vanagon GL