Cast Iron Drain/Soil Pipe Connector 4" X 1 1/4"

2° Slope Saddle Tap – 4" Pipe to 1-1/4" PVC (3D Printed)

This is a 2-degree sloped saddle tap fitting designed to add a 1-1/4" PVC drain connection into an existing 4" diameter pipe (cast iron or PVC) using a drilled access point.
I used this fitting to tap a furnace condensate drain into a cast iron drain pipe beneath a concrete floor drain, with the tap located above the P-trap.

The slope is built into the model to promote proper drainage without needing additional fittings.

Design Specifications

• Pipe size: 4" nominal diameter pipe
• Access hole size: 1-3/8"
• Slope: 2 degrees (fixed, non-adjustable)
• PVC connection: 1-1/4" PVC (glued)
• Thread size (nut & fitting): 33 × 2 mm
• Clamp opening: 35.5 mm hole
• Indoor use only

Materials (By Component)

• Saddle fitting (rigid): PETG-CF
• Threaded nut (rigid): PETG-CF
• Seal (flexible): TPU
  • Printed 1.6 mm thick
  • Installed on the exterior side of the pipe

The materials were chosen based on what I had. You can change them to anything you think would work better. PETG-CF was chosen for stiffness, temperature resistance, and dimensional stability. TPU was chosen for flexibility as a seal..

Print Notes (Important)

• The provided 3MF file has:
  • Reduced print speed
  • Layer height set specifically to ensure clean thread formation
• Do not increase speed or layer height for the threaded components
• Threads are designed to be snug-tight only
  • Do not over-tighten the nut

Required Tools & Supplies

• 1-3/8" diamond drill bit for 4" cast iron pipe
• 1-3/8" standard hole saw for 4" PVC pipe
• Light sandpaper (for surface prep of 4" pipe)
• Silicone grease or Super Lube (for seal priming)
• PVC glue (for 1-1/4" PVC connection)

Installation Instructions (Step-by-Step)

1. Mark the Hole Location

   • Confirm the tap location is above the P-trap

      

2. Drill the Access Hole
   • Cast iron: Use a 1-3/8" diamond drill bit
   • PVC: Use a 1-3/8" standard hole saw

   • Deburr the hole edges

      

3. Prepare the Pipe Surface
   • Lightly sand the exterior surface of the 4" pipe around the hole

   • Wipe clean of dust and debris

      

4. Prepare the Seal
   • Print the TPU seal at 1.6 mm thickness

   • Apply a thin layer of silicone grease or Super Lube to the seal

      

5. Install the Saddle Fitting
   • Verify orientation so the 2° slope flows in the correct direction
   • Insert the fitting into the drilled hole
   • Place the TPU seal on the exterior side of the pipe

   • Thread the PETG-CF nut onto the fitting

      

6. Tighten
   • Tighten the nut by hand until snug

   • Do not over-tighten — excessive force may crack the fitting, damage the printed threads, or distort the seal

      

7. Attach the PVC Drain
   • Glue the 1-1/4" PVC pipe into the fitting using standard PVC cement

   • Allow a few minutes to full cure before introducing water

      

8. Test
   • Slowly introduce water and inspect for leaks

   • Verify proper drainage along the sloped outlet

      

9. Cut Excess Threading

    

Notes & Limitations

• Designed for indoor use only
• Not intended for pressurized systems
• Intended for gravity drainage applications
• Slope is fixed at 2°