Filler neck and vent pipe in the yard is one clue.
No oil tank inside the house.
No tank inside, filler neck in the yard.
The easiest way is looking for oil pipes coming through your walls - theyare hard to miss.
Check on any pipes coming through the basement walls. Look outside where grass is yellowing or not growing at all.
Unexplained pipes going through the basement wall. Patchy or yellow grass above tank outside.
A metal detector. oil filter and shut off valve emerge from basement filler pipe and vent are not right next to wall outside you cannot find the oil tank inside
If you put an oil tank outside in a cold climate you need to buy kerosene in the winter, which is more expensive.
The easiest way to tell if an oil tank in buried on the the property is the presence of a vent and/or filler tube coming out of the ground on the exterior. They are both about 2" wide. Sometimes these are cut off so you can look in the basement near the furnace or boiler. You may see two 1/4" copper tubes coming through the wall or out of the floor. These are the oil supply lines. They can give you a clue where to look on the exterior. This is a good article on the subject.
1 - the height of the oil tank. 2 - Tank Gauge. 3 - If the oil tank is low pressure hydraulic system is malfunctioning and is not transmitted.
to read a oil tank you have to get a oil stick that its long and then put it in the oil tank
By light oil and chalk
If you live on an old farm or a residence that housed a lot of motor vehicles, there may be an oil tank buried in the ground that was used to fuel machines. These tanks can corrode over time and leech unwanted toxins into the groundwater, or one may be taking up space where you'd like to build. Either way, you can safely remove an in-ground oil tank with a few tools from the hardware store and one or two strong friends. it would be around 40 feet in ground