1st method (dry)
Discharge Tube
Use compressed air and a soft bristle paint brush to remove dust build up, etc..
Done
2nd method (wet):
Discharge Tube
Take it outside
spray the shit out of it with simple green (I prefer Krud Kutter, I fond it cleans krud better than simple green, only let it sit for at most 10mins while brushing)
Use a soft (good quality) paint brush to gently scrub basically all parts of the tube/chassis
Rinse it clean with a garden hose, dont be afraid, just dont use the spray full jet setting, just the open hose with ok pressure is enough.
Drain as much as you can by tilting, inspect and see if you need to spray/clean/brush a little more, repeat rinsing and draining
The hit with some compressed air to get as much water out as possible.
Then bake in the sun or make sure to put some good fans on it for like a day or 2 to dry it out. If you have a dehumidifier stick in the rooms with it also.
Hope it helps