General rules I have heard for run down lines:
1) Treat them like sewer lines, everything should flow downhill to the pit.
2) Install a cleanout/ rodding port at every change of direction. Make sure you can access all directions of the line. Minimize the number of turns in the rundown piping
We had one sulfur plant with the sulfur condensor drains on the bottom of the condensor and a horizontal rundown line coming out of a jackete pot under the condensor. The sulfur had to make two right angle turns to get into the rundown line. Worst of it was we had no way to rod directly through the two 90 degree bends. We hot tapped a new outlet into the condensor cover plate on the run and installed a new rundown line on the worst of the condensors and then replaced the rest of the cover plates with new nozzles at the next TA. Problem solved.