1. Inlet:
An Inlet is a pipe which is connected with a tank or cistern or reservoir, which fills it.
2. Outlet:
An Outlet is a pipe which is connected with a tank or cistern or reservoir, which empties it.
3. If an inlet can fill a tank in $x$ hours, then, part filled in $1$ hour $=\frac{1}{x}$.
4. If an outlet can empty a tank in $y$ hours, then: part emptied in $1$ hour $=\frac{1}{y}$.
5. If a pipe $A$ can fill a cistern in $x$ hours and another pipe $B$ can empty the full tank in $y$ hours (where $y>x$), then on opening both
the pipes, then, the net part filled in $1$ hour $=\left(\frac{1}{x}-\frac{1}{y}\right)$.
6. If an inlet can fill a reservoir in $x$ hours and another outlet can empty the full tank in $y$ hours (where $x>y$), then on opening both
inlet and outlet, then, the net part emptied in $1$ hour $=\left(\frac{1}{y}-\frac{1}{x}\right)$.
