Prefab steel buildings

YY1 said
I had to pay a $75 county fee/inspection to show that my building with no plumbing would work with my existing septic tank.

You might also want to check the setback.

In my area concrete can go right up to the property line, but any structure (other than a fence) must be 5 feet away.
Click to expand...

Also, in my area, adding a separate building to an existing septic, doesn't change the septic capacity requirements as long as the building isn't a dwelling. If you're in the building, then you're not in the house. You haven't put any extra "load" on the system.