Two year old condo we have downstairs unit on slab. Recently just flushing clear water will sometimes take two flushes. Water always goes down but sometime there is no strong push on first try. Periodically we get a sewer smell. The toilet sits tight (no rocking). I've tried bleach as well as using bleach in sink and tub. I've even poured down hot water from a bucket (that always works). The sink & tub do not appear to have a problem. All other sinks and bathrooms work fine.