A plumber observes that a newly installed trap for a floor drain is consistently losing its trap seal due to evaporation in a rarely used mechanical room. What is the most effective and code-compliant method to prevent this issue?

Question: A plumber observes that a newly installed trap for a floor drain is consistently losing its trap seal due to evaporation in a rarely used mechanical room. What is the most effective and code-compliant method to prevent this issue?

Answer options:

• Increase the trap arm length. ✅ Install a trap primer.
• Connect the floor drain to a continuous waste.
• Increase the size of the vent pipe.

Correct answer: Install a trap primer.

Explanation: To prevent the loss of trap seal due to evaporation in floor drains that are rarely used, installing a trap primer is the most effective and code-compliant solution. A trap primer automatically adds a small amount of water to the trap at regular intervals, maintaining the trap seal. Increasing trap arm length, connecting to continuous waste, or increasing vent pipe size will not address evaporation.