The t-case is simple, use the drain plug to drain the fluid and use the fill plug to refill.
For the diff(s) pull off the cover to drain, put it back on with either a gasket or sealant and refill using the plug.
If you have a manual trans it's pretty much the same deal as the t-case. If you have an auto, it's a little more difficult. Your best bet may be to take it and have it flushed. If you don't want to do that you just drop the pan, change the filter and refill through the dipstick tube.
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