- 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.