I'd say 5k per is low, 20+ is high.
Note here they require enough land for a second system in the future.

Consider something Green I've thought about, assuming the county / Stae allows it and you can find an engineer to design it.

Two systems, one regular, one for grey water.
Showers, bath sinks, washer ...

Takes the load (urrgh) off the main system.

Some extra plumbing, but may not be a major difference if done up front.

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1990 500SL

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