A manual transmission usually has a plug on the side of the transmission housing.
Manual Transmission Fluid Type. Manual transmissions take ATF, heavyweight/high viscosity (e.g., SAE 75W-90, 75W-140, 80W-90, 80W-140, 85W‑140) gear oil, synchromesh, or motor oil. Always check the owner’s manual.
Checking/Adding Manual Transmission Fluid. To check the fluid level you must turn the engine off, apply the parking brake, clean around the area, and then remove the plug with a wrench. The fluid should be level to the plug hole bottom. Fill as necessary. You may need a special adapter that fits on the bottle to transfer the fluid.