Yes, drain the used KBS Klean solution into a bucket and keep the KBS Klean solution until you can inspect the inside of the tank to verify it has been cleaned well.
You can filter the KBS Klean solution as it gets drained into the bucket to clean out the rust and junk from the dirty KBS Klean solution.
You can always re-use the KBS Klean solution if the inside of the tank needs additional cleaning. Some customers have cleaned their tank up to ten times which all depends on how dirty and nasty the inside of your tank is when you start.
TIP: Placing some nuts & bolts or loose chains inside the tank, along with frequent shaking and rotation with the KBS Klean solution, will help knock away loose rust and contaminants.
Please review the complete Tank Sealer Application Directions before beginning your project.