Increasingly difficult, Roger? If that's really so, the problem is almost certainly condensation. Clean it, shake it, clean it again, then shake it some more - full arm's length, as fast as you can and as broad an arc as you dare risk (best not done mid-session). In short, you need all the centrifugal force you can get. Finally cover every hole, cover the end on your knee, and blow wrongway through the mouthpiece as sharply as you can. (On reflection, this might be totally impossible on the Low D.) Even then, it might not be totally clear, but if condensation had indeed been the problem, it will certainly play a whole lot better after all this.