Hi new here love the game,
I work in the field as a technician who deals in remediation of oil tanks when they eventually rot out in the ground spilling their contents for unsuspecting homeowners to smell in their well water eventually.
Anywho, homes have heat sources (diesel tanks usually 250gal and 550gal, propane tanks etc) these are located either in their basements with a fill pipe channeled through the wall, above ground outside near the furnace location, or underground with respective fill and vent pipes sticking out. They have copper lines that feed fuel to the furnace and return copper lines that drip excess fuel back into the tanks.
What oil companies dont want you to do (which you can do absolutely I know people at my job that have done this) is use this home heating oil in diesel engines for vehicles.
Where else are these tanks located?
Farms have auxiliary tanks on their properties filled with both diesel and gasoline. These tanks are generally 550gallons. Larger farms have 1000gallon tanks.
Accessing: for ingame purposes syphoning gas from tanks works only if you can generate a gravity feed. Tanks above ground are used in this manner to feed furnaces in the home, they are not powered by electric pumps. Underground tanks would require digging to the top of it and cutting the tank open to access the fuel inside. These are also maintained by gravity feed.
Usage: obviously for vehicles but also for heating. Technically if you can fashion a home furnace to bypass the electrically powered burning and oil feed system you could have a basement furnace running off of the diesel heating oil tank. The tanks themselves are heavy and would be poor water collection containers unless throughly cleaned out. Now, the gauge is just a floating buoy that could be used to create a fishing bob.
Occurance: every home has a heating source. Rural homes always have diesel furnaces or propane. Suburbs will vary between diesel and propane and electric heat. Cities almost never have diesel furnaces but will be powered by city distributed propane or just electric air heater.
Game breaking? Is the ubiquity of diesel game breaking? If I were in an apocalypse I would absolutely go hunting for peoples oil tanks for fuel sources. Every house has one and most rural and suburban have diesel and propane fuel. For ingame carrying diesel would be slow and effortful if syphoned into a 5 gal bucket. Diesel is roughly 7lbs per gal *5 =35lbs. Accessing diesel via the syphon from the tank method would work great but even better for letting gravity already do the work for you by cutting the copper wires in the basement and draining the fuel out into a bucket. Some tanks even have pre-installed shutoff valves for servicing the furnace.
Tldr: just think the houses in the game need heating sources in service to realism.