Volvo Penta D4 Operator's Manual page 62

Maintenance. Freshwater system
Draining the fresh water system
Remove the filler cap on the expansion tank (to allow
the coolant to run out faster). Use a suitable receptacle
while draining.
There is a hose mounted on the intercooler. Move the
hose and connect it to the drain nipple (1). Open the
drain nipple by carefully screwing the nipple. Use a no.
17 block spanner if the nipple sticks. Drain all coolant
and screw in the nipple by hand.
Move the hose and then continue to drain the coolant
from the drain nipple (2) on the engine block.
NB! Leave the old coolant to a facility for destruction
60