A drip leg, also known as a sediment trap, is a short vertical section of pipe installed in the gas line just before it enters the furnace. Its purpose is to use gravity to catch any moisture, oil, or debris that might be traveling through the gas lines before it can clog the furnace's Orifice. This is a vital part of a professional installation for all Mobile Home Furnaces to ensure a clean and reliable burn. Without a drip leg, small particles could damage the gas valve, leading to a system lockout or a hazardous condition. You can find the necessary black iron or brass fittings for these traps in our Water-Plumbing section. It is a mandatory requirement by most local gas codes and is a hallmark of a high-quality Ducted Shop All setup. Regularly checking the cap of the drip leg during maintenance can reveal if your gas supply is particularly dirty. It is a simple, non-mechanical solution for long-term furnace health.