Dual fuel tank not used for a while, questions

[UATahoe]

I am looking at buying an 87 R10 that has dual tanks. The PO told me that she only used one tank and never filled the other tank up. She wasnt sure if the dual system was working or not. My concern is that this tank hasnt been used in a long time. I am guessing i will have to replace everything to get it back working properly? tank, pump, and more than likely the switch? Any input would be great. I am sure at one point the switch quit working and instead of fixing the PO just used the one tank, but i am guessing that sitting for so long without being used ruined the rest of the system.