I'm planning to flush my cooling system (1994 sl500) and have a few questions:

1. Is there a drain plug for the block ...if so, where is it located?
2. Should I run the heater during the flush or should the heater
hoses be disconnected and flushed with a garden hose?
3. Which heater hose is the input to the heater core and are
there any special valves (i.e., mono) that need to be
opened?

I appreciate any help/advice you folks can give me. Thanks.