I am the biological father of a child being adopted by the step father. How can I ensure an agreement to waive arrears after adoption will be executed

The best way to handle this issue is to have a formal writing between you and the biological mother and step father, where they agree in a writing that they are waiving all claims to child support from you and that they will waive all claims for all child support arrears and that they will direct the probation department to vacate all arrears from the account and close out the probation department account. Absent a formal writing signed by all parties that directs the probation department to vacate any claim of arrears and to close out its account will not get rid of the arrearages outstanding. If the adoption is finalized, from that date forward, the probation department will acknowledge that it cannot continue to collect child support but unless directed to vacate all arrears up to that point, those arrears will remain and be collected. You must have a formal writing signed by you, the bioliogiocal mother and the step father and it must be in numbered paragragh form telling them exactly what is taking place - they are not going to accept your claims or even what you say they agreed upon - if it is not in a writing and signed, they cannot simply accept it.