If memory serves me, only HST models have a screw on external filter. On mine, it is under the left fender. Looks just like a car oil filter, so it's easy to spot. If you have a manual tranny it may not have one. There is a filter screen on the suction line on the right hand side of the tractor. Follow the larger of the lines as it enters the tranny. Here you will find a large Banjo Bolt. Unscrew that and the screen assembly comes out. It will drain all your fluid, so have a 5 gallon bucket handy. It holds around 18 quarts...give or take.