My toilet does not empty the bowl with every flush. Older toilets can start to flush poorly because the jets around the rim that let the water out of the tank and into the bowl have become clogged with hard water deposits not allowing the water to exit the tank fast enough causing the toilet to flush poorly. And easy way to confirm this is what we call the bucket test. We simply fill a bucket with approximately 3 gallons of water and poor it directly into the bowl. If the water goes down rapidly and is left with very little water in the bowl then there is probably nothing obstructing the trap way of the toilet. You can try raising the water level in the tank but odds are the toilet will need to be replaced. The best way to prevent this from happening to your new toilet is to invest in a whole house water treatment system to keep the hard water deposits from forming again.