Pre-Algebra · Superchallenge problem

A tank starts with some water. During the 1st hour, $\dfrac{1}{2}$ of the water drains out. During the 2nd hour, $\dfrac{1}{3}$ of the remaining water drains out; during the 3rd hour, $\dfrac{1}{4}$ of what remains then; and so on, until during the 11th hour $\dfrac{1}{12}$ of the remaining water drains out. At that point $2.75$ liters are left. How many liters were in the tank at the start?