Dear Freak,
I'm glad you wrote; there has long been confusion about these two definitions. Why the confusion, you ask? Well, we could start with Merriam-Webster Dictionary and its no-fewer-than 21 definitions for "draft" and 5 for "tailgate." (An aside: Merriam-Webster notes that the earliest use of the word "tailgate" occurred in 1962.)
You'll notice, as I explain these complicated concepts, that it is difficult to have one without the other. If you will refer to Photo A (the one on the left... as a dog, I was unable to figure out how, using HTML -- the computer language used by bloggers to design their weblogs -- to label the two pictures), you will see Gladys "drafting"... that is, taking advantage of reduced air pressure created by the lead dog (me... although we all know that I have a high gear and I could quite easily shift into overdrive and drop her). In doing, she is also "tailgating"... that is, moving dangerously close to the lead dog. You'll know you are too close when all you can see in your range of vision is "tail" -- hence the term.
In Photo B (yes, Einstein, the
other photo), you'll notice me trailing at a much safer distance... at least one dog-length behind. As another aside, if the next frame were available, you'd see me performing a full-open-field-body-slam-tackle-takedown-rollover of Gladys. I just love doing that.
Hope this helps with your question.
Your friend, Oscar