Alyrics, I sure hope in your posting you meant that you dig a hole 12- 14 deep and then back fill it with some soil prior to planting your clematis. Although it is often recommended to plant your clematis deeper in the ground than it was planted in its container, planting a clematis 12-14 inches deeper in the ground is going way overboard and I sure wouldn't risk loosing a plant by burying it too deeply. Burying a clematis 2 or 3 inches deeper in the garden than it was in its pot is more what is typically recommended.

I have used something similar to your coke bottle technique on tomatoes but not yet done so on my clematis. Most of mine are planted in areas where soaker hoses or drip irrigations provide the water. For my tomatoes, I have taken a two or three liter bottle and drilled holes down one side of it spaced an inch or so apart. Then the bottle is sunk in the ground neck up so that the holes are facing the tomato plant. You can keep the cap screwed on the bottle until you want to water and then when you want to water, you just remove the cap pour water into the neck of the bottle and it fills the bottle and the water leaks out the holes slowly in the area of the roots. You could also add nutrients that way by pouring compost tea or alfalfa tea into the bottle.