Annual Retest List For your convenience, we offer an automatic annual retest list. At your request we will come out yearly when your backflow assembly is due, test the assembly, leave an invoice at your door (unless otherwise instructed). We also send the original report into your water district. As long as you are on our annual schedule your cost will always remain the same (never any increase), and always be done around the same time of year unless we hear back from you. Sign up and never be bothered with it again.