From my own experience on PW JT8s which we had to do periodically to recover performance.
Remove the generator cooling duct, blank it off. Disconnect the generator cables.
Have high power water hose on standby.
Dry motor the engine, when up to speed fire the hose down the intake for about 60 seconds, continue to motor to blow it through after water shut off.
Leave to drain for at least two hours.
Reconnect generator cooling duct and electrical cables.
Check start the engine and run for at least two minutes.
It's been a long time since I did this but that was the general gist. Clean water used, no cleaning agents.