Drilling Holes for Bulkheads & Uniseals

How to drill a tank for the Banjo bulkheads and Uniseal pipe-to-tank seals we sell. The hole sizes below come from the manufacturers' published charts for those exact part numbers. The fitting's size name (1/2", 1", etc.) is not the hole size.

Before you drillOnly drill a tank that is completely empty, rinsed clean, and open to air (not pressurized). Never drill a tank that has held chemical without fully rinsing it first. Wear eye protection and follow your drill and hole saw maker's safety instructions.

1. Pick the right fitting

Banjo bulkhead (threaded) tank wall gasket (inside tank, against wall) bulkhead flange nut (OUTSIDE) OUTSIDEINSIDE Uniseal (rubber seal + rigid pipe) tank wall wide side faces where the pipe comes from rigid pipe (sized by pipe OD) pipe pushed in from outside

Bulkheads clamp the wall between a gasket inside and a nut outside. A Uniseal is a rubber seal pushed into the hole; a rigid pipe of the matching outside diameter is then pushed through it.

2. Hole sizes — Banjo poly bulkheads

Our part Thread size Hole size (Banjo) Nut torque (Banjo)
Banjo TF050 1/2" FNPT 1-5/8" 15–20 ft-lbs
Banjo TF075 3/4" FNPT 1-5/8" 15–20 ft-lbs
Banjo TF100 1" FNPT 2-1/4" 30–40 ft-lbs
Banjo TF125 1-1/4" FNPT 2-1/4" 30–40 ft-lbs
Banjo TF150 1-1/2" FNPT 3" 60–70 ft-lbs
Banjo TF200 2" FNPT 3" 60–70 ft-lbs

Sources: Banjo 2025 catalog (Poly Bulkhead Fittings table) and Banjo Bulkhead Tips (torque). Shop Banjo bulkheads.

Banjo's install notesThe gasket goes on the inside of the tank. Seal the inside threads with a soft-set thread sealant; the outer threads do not need sealant. If the gasket bulges out, the nut is overtightened — overtightening can strip the plastic threads or crack the fitting.

3. Hole sizes — Uniseal pipe-to-tank seals

Uniseals are sized by rigid pipe outside diameterThe size name is the nominal pipe size (Schedule 40 / IPS). Check that the outside diameter of what you push through matches the pipe OD below.
Our part Uniseal model For pipe size Pipe OD Hole saw size (Uniseal)
3/8" Uniseal (32296) U038 3/8" 0.675" 1"
1/2" Uniseal (32324) U050 1/2" 0.840" 1-1/4"
3/4" Uniseal (32325) U075 3/4" 1.050" 1-1/4"
1" Uniseal (32326) U100 1" 1.315" 1-3/4"

Sources: Uniseal installation instructions, UniSeal hole size chart (Barr Plastics) and Uniseal data sheet (3/8" size). The 1/4" Uniseal (32295) is not listed here yet while we confirm its size. Note that the 1/2" and 3/4" seals use the same 1-1/4" hole.

4. Pick and mark the spot

  • Choose a flat area of the tank wall, clear of ribs, seams, molded lettering and corners, with room on the outside for the nut (bulkhead) or the flange (Uniseal) to sit fully flat.
  • Measure where the hose or pipe needs to run, then mark the hole center. Check clearance inside the tank too.
  • Re-check the table above for the exact part in your hand before cutting.

5. Drill, clean, and deburr

  1. Cut the hole with the hole saw size listed for your part.
  2. Remove all plastic shavings from inside the tank so they can't reach a filter or pump.
  3. Smooth the edge of the hole. Uniseal: "Ensure that the hole is cut clean, irregular holes could cause poor seating and possible leaks. Smooth out all burrs and rough spots around the hole with sand paper."

6. Install

Bulkhead: pass the body through with the gasket on the inside of the tank, thread the nut on from the outside, and tighten to the torque in the table. Do not overtighten.

Uniseal (from Uniseal's instructions):

  1. Place the Uniseal in the hole with its wide side facing the direction the pipe will come from (for a pipe pushed in from outside the tank, the wide side faces out).
  2. Cut the pipe end clean and square, then chamfer/bevel it (Uniseal says 15° minimum) so no sharp edge can cut the seal.
  3. Wet the pipe end with liquid detergent or soap. Uniseal says do not use silicone, grease or Vaseline.
  4. Push the pipe through from the wide side until it clears the inside of the seal by at least 1" (2" recommended).

Related: How To Plumb a Tank Bulkhead · Free Training Hub