They can not take a bath because the drain plug does not hold water. 

If you don't drain it, how much is catching 2 gal of water from a 40gal water heater going to help?

If it works and drains properly, then you know there is no problems with drain pipes and garbage pipes...etc. 

In my area for 25 lots, each having their own tank it's about $4k/septic tank+drain field so that would be about $100k, and I'm assuming a well would be about $30-$50k.

The disclosure mentioned the installation of a secondary drain field and the fact that the city was soon planning to connect the entire neighborhood up to city sewers (at some point ... whatever that means!).     

Does the basement have drains and bathrooms?

I'd hate to completely drain my account to pay cash for the RV, then still owe on the car.

Going through a loss of a parent is difficult and can be emotionally draining and in her situation, she may not have been completely cognizant of the financial responsibilities she's committing herself to cover her deceased mother's payments.

I have young tenants who does not know the difference between water supply pipes and drain pipes, totally clueless. 

I also run the water and check the drains for clogs and remind them that the lease says that if they clog it, they're responsible for unclogging it (they somehow always forget this).Good luck and get used to saying "no", your sanity will thank you.