@Darren Sager Using a drain coil type heat exchanger (perhaps 2-4 in parallel) is one option we are entertaining.

Another great way to save money and hassle is to put in your lease: if there is a clog in any of the drains at the rental unit tenant call the plumping company at his or her expense.

And the best part is is that I see why there has been a back up in the drain lines and it will be about 1/2 hour to fix and $20 in PVC piping! 

The water is crystal clear and a steady flow rate unlike a french drain system would be.

A house that old you also have older ungrounded wiring and cast iron plumbing drains to worry about.

This far I have done 1 flip and hold many rentals.Scope of work for a single family in PA2nd Floor Bathroom New tub and flooring and possibly drain and faucet replacement New vanity and fixtures Bedrooms and hall way Windows?

And if you haven't already decided not to run screaming, remember that HOAs can declare special assessments, so you may, indeed, be paying for new siding and roofing, storm drain issues, etc.  

Basically one thing all 3 said in common is that I need a new drainage system put in (a drain tile system and a sump pump).

Yes I have one and got it like everyone else but think about it, The cost of setting one up, tax returns for it and then yearly renewals, its more like a cash flow drain. 

Grease down the drain in a big no-no amongst other things that can clog them up.