Feeding only pinkies will still produce some wastes and urates, even if a bit less than when bulked up with fur - they are not 100% absorbed. However, the snake should be on half-grown mice at this stage. Even though it may be a bit smaller than many of the same species at one year, it is probable that it has been sparingly fed for the first year of its life. This will cause no problems at all in the long-term. Pink mice are only appropriate early meals for the smallest species, and those which have very small young, such as GTPs, but even then, as soon as they are big enough, they should be moved on to fuzzies and then upgraded as they grow. I don't think there is one species of python for which a pink mouse is appropriate for a 12 month old specimen. As far as passing wastes goes, it is usually an irregular occurance, and is dependent of temperature, activity, and to some extent, the foods which are offered.
Mike, I would say that a feeding regime of 20-30% of body weight, while tolerated by most species, is not conservative - it's at the high end of what would be recommended by experienced keepers, and definitely something to be cautious of doing in high summer. January to March it's far safer to be feeding smaller meals, especially if hot weater is imminent. While these are captive animals which can utilise much of what we offer them on a regular basis, 20-30% of bodyweight is of a magnitude many times that which they would regulary get in their natural habitat, the exceptions being when there are brief times of plenty such as during mouse plagues or particularly good seasons. I believe we should strike a balance between the two options, even to the point of not not feeding to a routine - skip a week or three occasionally, let the snake become really hungry sometimes. These are animals which are built to live with peaks and troughs in their metabolism, and it may be beneficial to allow their bodies the full range of metabolic reactions. If you offer 20-30% of a snake's bodyweight in food every week, it will be in a constantly switched on digestion phase 24/7.
Breeders of designer snakes pump their animals with food because they want them to breed as early as possible, the competitive nature of that game dictates the behaviour of the keepers to stay ahead of the competition and increase returns in the short-term... may or may not be a bad thing...
Jamie