A model is presented to simulate endloss from a high beta plasma contained laterally in a straight solenoid. For slender plasma columns, the plasma lifetime depends on both the acoustic transit time (time for a sound wave to traverse one-half of the plasma length), and the characteristic radial diffusion time (diffusion of plasma across the magnetic field). In the limit of strong diffusion (which occurs for narrow high beta plasma columns), the plasma lifetime equals the hybrid lifetime which is proportional to the geometric mean of the acoustic and diffusion times. This predicted behavior stands in marked contrast with conventional endloss theories which have confinement time proportional to acoustic time alone. It is also shown that the endloss process may be accelerated considerably if the ratio of plasma radius to magnet radius is not small, due to inverse mirroring effects in the streaming plasma.