i don't really understand why "your pal" thinks a stomach pump will help with constipation. Even if such a thing were available (which it probably is - people are strange!) a "stomach pump" brings things up from the stomach. Poo is too far down the GI tract to be bought up. Also, unless the poo is very liquid just think how wide a tube you'd have to get down your throat and past all the sphincters. If the poo is that liquid, and that high up your "friend" has a very big medical problem (bowel obstruction), for which he should seek help right away.
If the "friend" just has constipaton (and when i say "just" i am not trivialising it at all cause it can be an all consuming and very miserable condition) and finds that laxatives don't work as he'd like, it might be an idea to chat with his gp, because different laxatives or a change in diet/fluid intake might be considered