Rust is formed when iron is exposed to moisture and air. Outdoor barbecue grills are extremely susceptible to rust, especially in humid or rainy climates. Cleaning rust off of a grill may seem like an impossible task, but there is a tried and true way of dealing with this problem.
Combine the lemon juice, detergent and water in a bowl. Dip a grill scrubbing brush into the solution, then scrub the excess rust away from the grill.
Close the barbecue grill lid to prevent the solution from evaporating too quickly. Leave it closed for 24 hours, allowing the lemon juice to dissolve the rust.
Scrub the grill with the brush and solution once again. If rust doesn't come off entirely, wait another 24 hours, then repeat. Rinse the grill thoroughly with water and pat it dry with a towel.