This is easier said than done though as in my experience aspects of rent control regulation can and do change fairly frequently at the whim of the town's officials. 

There is one or two local REI clubs but not an official REIA that I've found

In fact, to remind myself of that, my official business model is "professional problem solver."

EP, as well as local township ordinances that could be in play.If the tank is out of service because it is deficient, many local municipalities will require that first it be pumped, they filled with stone and the lid broken to render it non-functional, then graded over and planted like in grass.In each PA  municipality there is an official called the Sewage Enforcement Officer, SEO, contact the township get the name and phone number of the SEO and call him or her for a direct answer to your situation. 

>Hopefully you have this in writing signed by both parties (Notice of Lease Expiration or some sort of document).Unfortunately I do not have an official notice signed by both parties, however I do have this in the form of an email that was sent to them.

But we've really been fortunate to have the support of a lot of great BP members (although we are not an official BP meetup - I'm not sure if it's possible to even have that designation?)

Could you install a catwalk, that would connect both of them and thus make it officially a 2-unit property, that 2 friends just happen to have split up to get their private space?

.- Then, I'd give the tenants official notice as outlined in the lease for inspections, normally 48hrs.

Its not official, but its going to be essentially the same thing, and most likely cheaper.  

Is there a special invoice or other form that I should be sending them to make it more official?