I have yet to fill outdoors, but I enjoyed expelling outside a number of times this fall.
We live in 10 mostly wooded acres. I have little difficulty retaining 2 qts so long as the solution is mild. Coffee is my favorite solution for one of these "enema treks." I take my enema in the bathroom fully clothed with just my pants down. As soon as I empty the bag I pull up my pants, stash the equipment, and hightail it out toward the tree line.
The excitement is such a charge. The fluid sloshing in my gut. The occasional cramp. The increasing peristaltic waves. On a few occasions I've managed to do a few chores while holding, but in short order I start a determined hike into the woods.
Once I find a pleasing spot, I brush back the duff to reveal some earth. Sometimes mossy, sometimes grassy, often raw soil. I drop my trousers. Sometimes I remove them and my boots, sometimes I leave them around my ankles. I lay down on my back and stare up and around at Mother Nature. I feel so dreamy lying partially filled and partially clothed.
When the time is right I let loose. I'm careful to raise my feet up, sometimes knees to chest, if I've left my boots and pants on. If I'm nude from the waste down im much more free in choosing my position.
Voiding on the soft earth is a wonderful feeling. The aromas of the expulsion mixed with the musky, mushroomy arboreal scents relaxes me further. The sensation of bits of forest floor stuck to my naked skin is titilating. I find myself moaning and sighing as the fluid is released.
If I am of the mood, sensual erotic massage of my manhood and ejaculation can be part of the process.
Temps here are now often in the single digits, so outdoor sessions will likely wait until spring, or at least for temps closer to freezing. I'm planning the logistics for an outdoor fill, but I must incorporate some stealth in hauling the gear out of the house. Reading through this great thread has helped immensely as I formulate and fantasize about my plans.