Others may and probably will say different, but unless you are using grips, you don't need to worry about covering the holes. I personally just use slugs, so I haven't had to worry about it. Most people I know that use insterts just taped their's up with duct tape. I only leave it in the water for about 20 minutes and repeat the process until I get the desired results, usually 2-3 times for each ball. I just use hot water from the tap and a little bit of dish soap.