Drain flush refill

[Swanybawanie]

Been reading in the manual about “drain, flush, and refill” on the direction Reverser, hydraulic systems, transmission, final drives. Flushing is all new to me. Here are some questions:
1. How do you flush?
2. What are used?

[Lavoy]

Kerosene or diesel fuel typically, never gasoline.
Reverser you can drain, fill with whichever, start the engine, shift reverser to forward and backwards a few times, shut off and drain and refill with HyGard or equivalent.
Hyd system, drain, fill with whichever, start engine, do not touch hyd valve, only let the system circulate, shut off, drain, refill with hyd oil.
Trans you can drain, fill with whichever, put pto lever in gear, let idle for a while, drain and refill. If you choose to drive it, only short distance, slowly, no load. Refill with GL5 gear lube of choice.
Finals, drain, fill with whichever, you will have to drive the crawler some, but again, back and forth only, no steering, no load, no high speed. Drain and fill with GL5 gear lube of choice.
Lavoy