how to check and change the manual Transmission Fluid?

how can i check the level of manual transmission fluid ??
i can only see a black rubber plug on the top. when i unplug it, i didnt see a stick or anything that i can check.

Also, i have read another forum people said add about 2.5 quarts to b-series will be enough.
so how much is "2.5 quarts" in litre or ml??

To check the level, open the fill plug on the side. Stick your index finger in the hole and bend the first part of your finger downward. The rule of thumb is if you touch oil, it's ok; if not, you need more. As for the conversion, try google.