Pool Plumbing Basics: Pipe Sizing, Layout, and Common Mistakes

Pool plumbing is one of those skills that separates builders who do good work from builders who do great work. The homeowner never sees the plumbing — it's buried in concrete and behind equipment pads. But they feel it every time the pool doesn't clean properly, every time the pump cavitates, and every time the energy bill comes in higher than expected.

Suction side plumbing

The suction side runs from the pool to the pump. It includes the main drain, skimmer, and any other suction fittings. The suction side is the most critical to get right because this is where cavitation occurs — and cavitation destroys pumps.

• Suction pipe should always be at minimum 2" for residential pools; 2.5" is preferred for longer runs or higher flow requirements
• Keep suction runs as short as possible — every foot of suction pipe adds friction, and the pump is working hardest to pull water uphill
• Avoid 90° elbows on the suction side wherever possible — use 45s or sweep elbows to reduce friction
• The main drain and skimmer are typically manifolded together with a 3-port valve so the operator can balance the draw between them
• Minimum 2 suction ports (dual main drains or main drain + skimmer) per the ANSI/APSP drain entrapment standards — single main drains are not code in new construction

Return side plumbing

The return side runs from the pump through the equipment and back to the pool. Since the pump is pushing (not pulling) on this side, friction is less likely to cause cavitation — but it still affects TDH and energy consumption.

• Return pipe is typically 2" for residential pools; size up if running long distances to multiple returns
• Return fitting placement drives circulation pattern — think about where dead spots might form
• Returns should generally be aimed downward and slightly toward the main drain to encourage circulation across the pool floor
• For pools with attached spas, the spa and pool share suction and return plumbing but require separate valves for independent operation

Main drain requirements

The Virginia Graeme Baker Pool and Spa Safety Act (VGBA) requires all pools to have suction outlet systems that prevent entrapment. For new construction this means:

• Two main drains separated by at least 3 feet (center to center) — or one compliant single main drain with an alternative design
• VGB-compliant drain covers rated for the flow rate of your system — check the cover rating against your pump's GPM at low speed
• Covers must be secured with screws — not just snapped in place
• Cover replacement intervals are printed on the cover — typically 5–10 years

Pipe material: schedule 40 vs schedule 80

Most pool plumbing uses Schedule 40 PVC. Schedule 80 has thicker walls and higher pressure ratings — it's typically only required in specific applications like suction side runs near the equipment pad, or in commercial applications.

All underground joints must be solvent-welded (glued), not threaded. Above-ground connections at equipment can be threaded or union connections. Use unions at every piece of equipment — you'll thank yourself the first time you need to service the pump.

The most common plumbing mistakes

• Undersizing suction pipe — #1 cause of cavitation issues
• Long suction runs with multiple elbows
• Not using unions at equipment — makes future service extremely difficult
• Improper bonding of metallic fittings and equipment — a code and safety issue
• Return fittings aimed at the wall instead of angled to promote circulation
• Forgetting to pressure test before backfill — a leak under the deck is a nightmare to find later