During this process, residents may experience a rumbling sound, in addition to the possibility of water entering your sink, bathtub and/or toilet. Sewer lines can develop air pressure or a partial vacuum from the cleaning process. Usually any excess air pressure or vacuum will dissipate through the plumbing vents, but occasionally there are facilities with inadequate plumbing vents (i.e.: no vents, undersized vents or obstructed vents). In the case of inadequate venting, air pressure could escape through the toilet, floor, sink, tub or shower drains, causing water to splash out or, a vacuum could draw the water out of the fixture traps allowing unpleasant odors.