I know this isn't a professional recommendation. But I have run into too many defective tanks and bowls that just want to drip at the bolt holes or the fill hole washer. When this happens, it tends to be incorrect curvatures. Maybe one of the bolt holes are too close to the bottom corner of the tank where it curves upward preventing a good flat seal for the rubber washer, or the fill hole in the bowl is not round or flat enough for a new rigid rubber seal to do it's thing. and maybe over time these washers and seals will seat but getting a drip shortly after assembly is just embarassing. I don't want to risk overtightening the bolts to compensate for sloppy ceramic work by the manufacturer. So I have gotten in the habit of cheating and using clear silicone on the bolt washers and fill hole seal when assembling a tank to a bowl. It elminates the drip problem on new assemblies and my hope is that over time, the rubber seals will seat better on their own eventually. Any insights on this?