Once the doors are shut, all the PCs, Custodio, and Mutt must make a DC 15 Fortitude save or become nauseated. The DC for the ex-guards are higher (DC 20) since they have been there longer but each of them gets a +4 circumstance bonus to their rolls because they had access to food, wine, and water. PCs that eat rations and drink water from waterskins gets a +2 circumstance bonus to their rolls.
On a successful save, the character is simply very hungry and thirsty and must eat food and drink water within 1 hour or start to feel light-headed. If they go longer without food or water they become fatigued within 1d4+1 hours.
On a Natural 1, bad things begin to happen inside a character's gut. There is an urge that can't be delayed.