Explain the following:

Two holes are made in a completely filled sealed tin can to take out oil from it.

Two holes are made in a completely filled sealed tin can to take out oil from it because there is no air inside a completely filled and sealed oil can. When the can is tilted, the pressure due to the column of oil (inside the can) at the hole is much less than the atmospheric pressure outside the can, so the oil does not flow out of the hole.

But if one more hole is made at the opposite end on the top cover of the can, air from outside the can will enter in through this hole and will exert atmospheric pressure on the oil from inside along with pressure due to oil column.

This results in the increase in the pressure on oil, and so it easily flows out through the hole of the can.