I have a Gerber toilet in my downstairs bathroom that flushes twice every time I flush it. The bowl empties, refills, empties again, and then refills again. I believe it is the original toilet from when the house was built in the early nineties. Any suggestions on a possible fix for this? The toilet has no other problems so I don't want to shell out the cash to replace it. I just don't like paying for water that I'm not using. Thanks!