Thoughts on buying a property with a shared septic from 1961

[Sean Keating]

I'm looking to buy a house hack and I found a property that I am interested in in Washington State and I'd hope to sell this one within 3-5 years.  My concern is that because of the septic's age, there might be a large cost coming down the line.  The sellers have mentioned that it was inspected and cleaned in Dec 2016.  Also, it is shared with one other house owned by others.  Should I be concerned with that as well?

Anyone thoughts or insights you could share on how you would make a decision on a property with a septic of this age?