The algorithm to estimate pile-ups is basically the same as epileupmask (see its document for detail of the algorithm; that also describes the limitation in the estimate of pile-ups).
This task eootepileupmask offers some command-line options so that a user can get a piled-up pixel mask file etc., in addition to the OOTE mask etc. so that users do not have to run epileupmask again just to get them.