Hi, I recently had the Drake CST776CSFG 2-pc 1.6g toilet installed & after the toilet has been flushed the water in the bowl drains out to a very low level within about 4 minutes. I marked the levels in red on the attached photos. The toilet has just been in place a few days & has only been used once or twice because the rest of the bathroom work isn't finished. What might be causing this & how do I fix it? Many thanks!