Q. My clients want to add a disposal during a remodel of their 1950s kitchen. The 2-inch waste line runs at a shallow pitch for about 30 feet (with three right-angle bends) before diving into the main 4-inch cast iron line. Over nearly 50 years, they’ve had only a few clogging problems with this waste line and had to ream it from the clean-out. Will the disposal cause this line to clog more often?

A.Master plumber Rex Cauldwell responds: Yes, the line will definitely clog up more often. In my experience, having a shallow pitch for 30 feet is asking for trouble — especially on a kitchen drain line, which is more prone to clogging anyway because of all the grease and food solids it has to carry. For one thing, the pipe is rarely set dead straight, but instead tends to wander slightly up and down, which speeds up the clogging process.

Before installing the disposal, I would either increase the slope of the pipe or increase its size to 3 inches. Either strategy has its difficulties. Increasing the slope of the pipe often requires cutting joists, which may not be possible. Increasing the pipe size will require cutting in a new tee on the main cast iron line — which is not an easy job. I use steel-cutting circular saw blades to cut cast iron, and finish up the cuts with a metal cutting blade on my recip saw. I then use Fernco fittings to splice in the new tee.