*Inlet:*A pipe connected with a tank or a cistern or a reservoir, that fills it, is known as an inlet.*Outlet:*A pipe connected with a tank or cistern or reservoir, emptying it, is known as an outlet.

- If a pipe can fill a tank in
*x*hours, then:

part filled in 1 hour = 1 . *x* - If a pipe can empty a tank in
*y*hours, then:

part emptied in 1 hour = 1 . *y* - If a pipe can fill a tank in
*x*hours and another pipe 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 = 1 – 1 . *x**y* - If a pipe can fill a tank in
*x*hours and another pipe can empty the full tank in*y*hours (where*x*>*y*), then on opening both the pipes, then

the net part emptied in 1 hour = 1 – 1 . *y**x*