A pump features a liquid sensing device (LSD) in combination with a housing. The LSD senses the level of a liquid collecting outside the pump and turns the pump on/off for pumping the liquid. The housing includes a housing wall to contain the LSD. The housing wall has an outside wall surface with an outside sensing surface. The housing includes an inside mounting structure to mount the LSD inside the housing in relation to the outside sensing surface. The outside sensing surface has ribs extending or projecting outwardly away from the outside wall surface in order to prevent an object from being stuck on the outside sensing surface, and allow the LSD to sense the level of the liquid collecting outside the pump and touching the outside sensing surface, reducing a malfunction of the pump due to the object contacting the outside sensing surface.