A makio is pretty much the same as the back slide, with two minor differences. The first and obvious one is that your sliding foot is doing a soul slide on the rail. The second difference is that you don't need to turn your body perpendicular to the rail to soul. You can just keep going straight ahead and it'll work fine.

Being able to do soul grinds is a big help when trying to learn this trick because being able to lock in the soul foot is a skill that takes a bit of practice to acquire. In any case, you approach the rail just like you are going to do a soul grind. Make sure you jump up high and get your weight on top of the rail. Lock in the soul foot and away you go. The free foot can be doing any number of things, but a typical action is for it to be either grabbed by a free hand or placed next to the souling foot. Soul like normal and hop off of the rail. The beauty of this trick is that it is an easy extension to soul grinds because a proper soul grind has almost no weight on the lead foot. And since little weight is placed on the lead foot, it is easy to take it off. The only hard adjustment to make is balance. For many, the lead foot acts as a rudder and guides you down the rail. However after a bit of practice it becomes easier.

So remember to jump high, get your weight over the rail, lock in the soul foot solid, and ride it out.. Good luck, and remember no rail is too long!