At Orbit Baby we don't have a need for an expired seat currently. Our recommendations for expired or unusable seats are to:
1) Contact your local recycling facility and see if they accept old car seats. Some facilities will accept them if they have been broken down and all the padding and is harness removed. They would be better able to direct you on how to prepare the seat for recycling.
2) Break down your car seat before disposing of it to ensure that no one will pick it up and attempt to sell or use the seat. We recommend cutting out the harness, removing all the padding and seat covers, cutting off the LATCH system, and writing 'DO NOT USE' on the car seat and base.