as shit

does not mean "like shit", instead it means "extremely"

He's (as) drunk as shit. = He's extremely drunk
In most cases, the preceding (as) is omitted.
She's dumb as shit.

If something is similar to "shit" literally, use "like shit"

That smells like shit!

In hiel soad (of in hiel soad mjitte).
Bygelyks:
"Se is sa dom as wat." — "She is dumb as shit."
"Hy is sa swak as wat." — "He is weak as shit."