Jerry M. has posted that the older M-15s were built  to use a certain pottie.  Then the pottie makers changed the shape slightly, which meant the pottie no longer fit.  He suggested heating the base of the pottie with a hair dryer then fitting it in place.  I did not have much luck with the hair dryer, and used waster at about 140 degrees F.  It took maybe half a gallon.  I pushed the pottie as far as it would go then poured in the warm water.  Assume the proper position sir and you will have a custom fitted pottie!