The minimum seal depth on a trap must be between:

The minimum seal depth on a trap is crucial for ensuring that wastewater does not escape into the living space while still allowing air to ventilate the plumbing system. A seal that is too shallow can lead to the siphoning of the trap, allowing sewer gases and odors to enter the building.

The recommended range for minimum seal depths is indeed between 2 inches to 4 inches. This depth is considered optimal because it provides a sufficient barrier against gases while also being deep enough to maintain the trap's functionality under various conditions, including changes in pressure and flow. Ensuring that the seal depth meets this standard helps in maintaining a healthy plumbing system and reducing the risk of health hazards associated with sewer gas exposure.