@Coleman ClarkAs a former owner of an Environmental Abatement company (operated in California), I have a bit of background on this subject. 

Current financial statements and of proposed transferee and its principals, along with credit reports, real estate experience and background for each 3.

I come from a highly technical/engineering background which I could fall back on to perform a significant amount of the maintenance and operation.  

Property manager put tenants into your apartment without background check, and we had to evict most of them for non-payment, harassing us, etc.? 

My property manager has no problem with this and gives me a call to provide some background on those top contenders (i.e. types of pets if any, special circumstances, potential red flags, etc.).  

You can still do a full background check on your renters.It sounds like you have essentially made a duplex out of a SFH.  

I would like to draw on my background which includes a bachelor's degree in Mechanical Engineering, control system design, sales and proposal writing.

However, this new buyer is threatening to get attorneys involved because he seems to think that this is not a encroachment granted in perpetuity.I think my folks are in the clear on this due to the nature of the language in the agreement but the last thing I want to have happen is get lawyers involved and have them have to pay to move the tank since, technically speaking, they are in the wrong.Don't have any experience/advice in this matter?

And I'm right next door to Euclid, but technically still in the city of Cleveland.

There were a LOT of hours the owner paid for that were spent doing the paperwork and background work involved.