Response on the photo of MeTo's engine with valley drain tube posted above:
The valley drain tube is just a 3/8" 90 degree elbow and about 10" of tubing. The elbow is a little unique in that it has a 1/2" fitting rib (see pic) soldered on the outside of the 3/8" elbow solder connection that goes into the valley drain hole. That feature provides a very snug (tapped it in with a hammer) fit in the valley hole. I did put some red Loctite on it to ensure a good seal. Because I extended the tube into the drain hole in the bottom of the block, the tube can't go anywhere. The rear cover on the back of the block also protrudes over the tube, thereby eliminating the possibility of the elbow vibrating out of the valley drain hole. That tube is very secure!