Is it likely to get ecoli or stomach bug from performing analingus on your partner who isnt sick or showing symptoms and just showered?

Technically, yes: It would be possible to contract E. Coli by analingus, but only few strains are problematic. Other intestinal infections like giardiasis and amebiasis can be sexually trasmitted in this way. Typical sexually transmitted germs, like gonorrhea and others, can be contracted if there is proctitis from infection caused by ano-genital contact. These must also be considered when practicing safe-sex.

Its possible: Eating and digesting fecal matter has been known to cause illness. As E. Coli is a common bacteria, the possibility is there considering how much was ingested. Despite the area being clean, passage of stool through the intestinal secretions harbors a risk. Good luck.