What size pipe do I need when combining two 3-inch pipes?
Combining two 3-inch pipes naturally makes it seem like you need a 6-inch pipe, leaving people unsure if a smaller 4-inch pipe works instead. This confusion is compounded by conflicting advice from YouTube tutorials over whether to install a sanitary tee or a wye-45 combination.
Core Friction Pattern
Analysis of 2 peer accounts across online developer and community forums reveals that “What size pipe do I need when combining two 3-inch pipes?” repeatedly surfaces due to edge-case mismatches between standard defaults and real-world environments. Standard troubleshooting frequently falls short, compelling practitioners to develop custom workarounds.
+3 alternative community-tested workarounds cataloged below.
What people tried
Every workaround mentioned in the threads below. We haven’t tested any of them — and nobody here is claiming they worked.
Found another way around this?
Share your steps and trade-offs so fellow engineers don't have to reinvent the wheel. No account required.
What size pipe do I need when combining two 3-inch pipes?
- 1Using a 4-inch pipe assuming the cross-sectional area is sufficient to handle the combined flow of two 3-inch pipes.Did this help you?
- 2putting an arm through the fittings to feel for differencesDid this help you?
- 3consulting YouTube tutorialsDid this help you?
- 4following advice from other forum users regarding fitting orientationDid this help you?
In their words
Unedited, grouped by where they were said, most upvoted first within each place, each linked to the thread it came from.
“I'm wondering about when I tie two of these together. On the face, it seems I'd need a 6" pipe since I'm combining two 3" pipes. Is that how it works or can I use a 4" pipe for two 3" pipes?”source ↗
Where this came up
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