How long can home fuel grease be stored? i have an grease furnace. it works fine but the current cost...

i have an grease furnace. it works fine but the current cost of #2 deisel and/or home fuel oil is bloodbath me. i can go gain about 500 +/- gallons out of an underground storage cistern (UST) for free. (yes, i have the owners permission)

here is the shut in... it has be sitting in the UST for 4~5 years. what are the issues/problems next to older fuel and would you try this near your own furnace?

i have the proper pumps/drums to transport the fuel, i in recent times need info nearly fuel oil sitting for long period of time.
thanks a bunch.
What is the element of pressure?
Answers:    It should be ok, similar to the other guy said be sur you have a filter and dampen seperator. Even tanks beside no leaks will own some water from condensation.
Clogged toilet?
IT SHOULD BE OK