The reason that you may not see parasitic remains in the toilet is simple: Generally, they are reabsorbed within the body (broken down) on their "way out". I believe that only the largest parasites may survive in any way intact, and then only if they died in the lower gastric regions shortly before a bowel movement.
Organisms have reasonant frequencies. If you match an organisms reasonant frequency for a given period of time by electrical means, that organism will certainly die. Most types of organisms have different reasonant frequencies, and a properly made zapper will hit on a good many of these.
Hope this helps/restores faith,
Richard Grieve