To give you an idea on the cost to remove the UST and get a No Further Action letter from NJDEP you would have to hire a pre-qualified environmental professional to investigate and remediate unregulated underground. 

Phase 1 Environmental Assessment & Sewer Line inspection

Environmental:  You may need Pollution coverage depending on the property and what is being done. 5. 

.), Radon, or other environmental issues10. 

It was listed as an environmental hazard on form 17 (seller disclosures).

. #2 - I am not an environmental expert or an attorney, but this one may be of concern.

For Sewer Scope I often use Root Excavation or Alpha Environmental and have had good results with each of them. http://www.rootexcavation.net/ https://alphaenvironmental.net/Hope that helps! 

It is being fully understood that except as specifically set forth herein, Grantor has made no warranties, express or implied pertaining to said property, the condition thereof including but not limited to, matters relating to environmental conditions or hazards on the property"Then later on its says " We are the sole owners of the premises and have good right and title to convey the same in manner aforesaid, and that they are free from every encumbrance, except as aforesaid and WE hereby Warrant and Defend the same against all lawful claims....."

on your first post, regarding the MH that is a tear-down, probably indicatesthat it's septic may be needing major work or replacement up to new codes,may be just as costly or perhaps more than new, with environmental disposalissues, etc.

I am an environmental engineer who designs water and wastewater systems..