New RO/DI unit

[Hangfire]

Hello all, and Merry Christmas. Hope Santa was good to everyone this year

I bought an RO/DI unit a little while ago and just got it all set up and running. I was wondering how much water to run through it before using the water in my tanks? I flushed the system with around 5 gallons and have made 4 more gallons of water, but want to make sure I have good clean water before adding salt and adding it to the tanks. Should I just check the TDS to see if it's okay?

Thanks for help.