Water flush and start up

Our van is some 20yrs of age, I have freed up the water filter(took a while) and will soon be commisioning the system. The seller drained it for us before winter. The old filter was green, yuk. We have a new water tub, and I have bought a new filter. The question is how we flush the system/pump? Do I run a week mix of bleach through it, and after flushing with frsh water then pop in the filter? That's the plan at present??