Drainage & Waste Systems | Learn on Patio

P-Traps & Venting Basics

A P-trap holds a small amount of water that seals the drain line, preventing sewer gases from entering your home.

A vent pipe allows air into the drainage system to balance pressure and prevent the trap from siphoning dry.

• Trap seal: Water barrier against odors and gases
• Vent purpose: Equalizes pressure so wastewater flows smoothly
• Wet venting: Uses one vent for multiple fixtures in small runs