Finally lowered my sink drain after two plumbers ghosted me

I had a similar headache last summer when I swapped out my old shallow sink for a deep Kraus basin. The garbage disposal ended up sitting about three inches below the wall drain, and looking at that heavy cast iron stack behind the cabinet was definatly the scariest part of the whole renovation. I used a Diablo Carbide blade on my reciprocating saw to get thru the iron, but man, those sparks were flying. I ended up using Fernco Proflex shielded couplings to transition from the old metal to the new Schedule 40 PVC. One thing I learned the hard way was to support the upper section of the stack with a riser clamp before cutting; otherwise, you risk that heavy pipe shifting or dropping, wich can cause leaks on the floor above. Getting the slope right is the real trick. I aimed for a quarter-inch drop per foot, but in those tight cabinet spaces, even an eighth-inch makes a difference for the disposal to clear. It’s a messy, sweaty job, but saving that $400 plumber fee felt pretty good once the water finally stayed inside the pipes.

I went through this when we put in an Insinkerator Evolution Excel. Instead of just cutting, I had to be super careful about supporting the upper portion of the cast iron. That stuff is incredibly heavy, and if it slips down even a fraction of an inch when you remove the section for the new sanitary tee, you're looking at a nightmare in the walls upstairs. I used a couple of riser clamps braced against the cabinet floor to keep everthing stable before I even touched my saw. For the actual connection, I skipped the standard glue-in PVC T-junction and went with a heavy-duty Fernco Proflex shielded coupling. The steel band on those gives a much more solid transition between the old iron and the new Sch 40 PVC than a basic rubber boot. It also helps dampen the vibration when the disposal is running, which is a big deal since that cast iron can carry noise through the whole house. I ended up dropping my outlet about five inches to get the pitch right, and making sure those bands were torqued down to 60 inch-pounds made all the difference for a leak-free seal.

You're right about the weight, but one thing often missed is deburring the inner rim of the cast iron after the cut. Even with a clean carbide slice, that internal edge is usally sharp. I always grab a half-round file and smooth out the inside diameter before the shielded coupling goes on. If you leave those burrs, they catch hair and grease, wich leads to a nasty clog right at the junction. It's a quick step that keeps the disposal from backing up later on.

Quick update — I took the advice about deburring the cut edge. I grabbed a half-round file and smoothed the inside diameter of the cast iron before sliding on the coupling. It really made the transition feel much more secure. The stack didn't budge either, wich was a relief. Everything is bone dry and the disposal is finally working like it should. Thanks for the tips!