Required to keep septic tank in ground?

[Lisa R.]

Hello again – Does anyone know if we are required to keep our unused, decommissioned septic tank in the ground instead of having it removed? I am selling a property where the buyer is putting a home on it and wants to remove it.   I was told by a company that in Washington state, we are required to decommission them, break the lid, fill them up with gravel and keep them on the property, although they did recommend not putting a house directly on top of it…

Does anyone have any experience with this?
or possibly could anyone tell me what they paid to connect to their city sewer?

Thank you again so much!! 
Happy Friday!! 
Lisa