Would be dig catholes, pit toilet and septic tanks.
Cathole can be build like crop zones, instead "growth" it will "decay".
Pit hole can a storage that when descontructed it drop waste barrels.
Septic tanks can be like a battery discharging, but when overloaded it spawn feces.
Infestation event can be allowed inside the pit hole and septic tank.
Maybe a Bugwise cockroach miniboss.

What do you think?