Does the size of a hole in a container affect the rate of effusion?
A small hole is used. Knudsen conducted experiments similar to  Graham's but approximately 50 years later (in 1909) and used a 0.025 mm diameter hole in a platinum strip of 0.0025 mm thickness. It was observed the size was not critical as long as the mean free path of the gas was ten times larger than the hole, thus the gas was at low pressure. 

In these experiments the gas is allowed to stream out of a small hole in the vessel into vacuum. The velocity of the escaping gas is just that of the trapped gas, that would be obtained if the hole was not there, and these velocities would be the molecular velocities. Thus the size of the hole must not disturb the distribution of molecular velocities, achieved by being smaller than mean free path.