When making a 20 inch offset in a 2 inch waste stack using PVC DWV pipe and 45 degree fittings, the length of the pipe between the two 45 degree fittings minus the 3/4 inch insertion depth for each 45 is

When making a 20 inch offset in a 2 inch waste stack using PVC DWV pipe and 45 degree fittings, the length of the pipe between the two 45 degree fittings minus the 3/4 inch insertion depth for each 45 is

• A. 28 Inches
• B. 26 Inches
• C. 26 3/4 Inches
• D. 25 3/4 Inches

Answer: (C)

The idea tested is how to size the diagonal run between two 45-degree fittings to achieve a given offset. When you use two 45-degree fittings, the straight section between them lies at a 45-degree angle, so its length is longer than the offset by a factor of sqrt(2). To get a 20-inch offset with that diagonal, the length of the straight piece between the fittings is 20 × sqrt(2) ≈ 28.284 inches. However, each 45-degree fitting consumes 3/4 inch of pipe inside it, so you must subtract 0.75 inch for each fitting. That’s 1.5 inches total. Subtracting gives 28.284 − 1.5 ≈ 26.784 inches, which rounds to 26 3/4 inches. So the length, accounting for insertion, is about 26 3/4 inches.

The idea tested is how to size the diagonal run between two 45-degree fittings to achieve a given offset. When you use two 45-degree fittings, the straight section between them lies at a 45-degree angle, so its length is longer than the offset by a factor of sqrt(2). To get a 20-inch offset with that diagonal, the length of the straight piece between the fittings is 20 × sqrt(2) ≈ 28.284 inches.

However, each 45-degree fitting consumes 3/4 inch of pipe inside it, so you must subtract 0.75 inch for each fitting. That’s 1.5 inches total. Subtracting gives 28.284 − 1.5 ≈ 26.784 inches, which rounds to 26 3/4 inches.

So the length, accounting for insertion, is about 26 3/4 inches.