Ever since Marvel Legacy launched, Frank Castle has redefined what it means to be a one-man army. In The Punisher comic series by Matthew Rosenberg and Guiu Vilanova, Frank has strapped on a different kind of battle gear: the War Machine armor, with a newly minted white skull on its chest. Now, Frank has more than enough firepower to back his war on crime, and he's taken his fight straight to Chernaya, a rogue Eastern European country ruled by a militaristic dictator.
However, simple soldiers aren't the only enemies that Frank encounters along the way. There are also a few ex-S.H.I.E.L.D. soldiers who each have their own specialized Stark-designed combat suits. In Issue 221, the most recent of the series, we learn of a new ability these suits possess, and it just so happens to be one that was introduced in the Marvel Cinematic Universe.
While out on a long patrol in the forest, one of the Iron Man suit-wearing ex-S.H.I.E.L.D. soldiers reveals that he can actually relieve himself in his suit, and that the urine goes through a water-filtration system which recycles the water back into the suit's hydration system. Choosing to avoid consuming that water, the soldier instead opts to go to the bathroom the old fashioned way.
If this function of the Iron Man armor sounds familiar, it's because Robert Downey Jr.'s Tony Stark first mentioned that special ability back in 2010's Iron Man 2. Viewers might recall the scene during Tony's birthday party, where Tony, after having a few drinks too many, tells Pepper all about his suit's newest urine-filtration system. Then, in front of all his guests, he relieves himself to cheers and applause.
Since all the S.H.I.E.L.D. armors have this feature, it's a safe bet that the War Machine armor, the most advanced and lethal in the fleet, has that same filtration system -- meaning that there is nothing that can stop Frank Castle, not a bathroom, or dehydration.