A wide tank of cross-sectional area A  containing a liquid to a heightH , has a small orifice at its base of area a  (a<1) :

Let h  be the instantaneous height of the liquid in a tank. Then, the instantaneous velocity of flow through the hole is,v=2ghUsing equation of continuity,A(−dhdt)=av=a2ghor, −∫+HH/ηdhh=aA2g∫0tdt∴  t=(Aa)2g(H−Hη)