I must be the only person using MEP around these shores and since I found an answer to my predicament, it is only fair to post it.
PROBLEM: When we star ROUTING from a pipe by clicking its centerline, MEP give us the choice of Wye junction piece to use next, however, it always default to a horizontal branch out. No choice of branching out at a given slope.
SOLUTION: If you want to branch out -left or right- other than horizontally, do not start routing.
Place the connecting part manually.
Use the Rotation parameter to indicate the outgoing degree angle of the outgoing line.
Follow by placing manually a piece of pipe with the same rotation angle as the branch.
Only then, start ROUTING.
Until you finish the route, all the pieces will be at a constant slope.
All this could be solved if at the time we start routing from the centerline of a pipe, we are given a choice of "BRANCH ANGLE or ROTATION or something to that effect.
Thanks to the guys at GRAPHISOFT USA for their help and patience.
Win 10 Home Premium - AMD Phenom IIX6 1090T Processor 3.20 GHZ 8.00 GB RAM 64-bit Opp. Sys NVIDIA Quadro 4000 AC 22, MEP