Septic system in a duplex rental

[Bienes Raices]

I was thinking of making an offer on half a duplex that's on a septic system (the other side of the duplex is a rental owned by another landlord). Are the septic systems usually separate for each side in a duplex, or joined? I'm not sure if I should pass on this because of the risk that the people on the other side might not be responsible enough.