Stop the toilet-bowl rock
If the toilet bowl moves when you sit on it, sooner or later the seal around the toilet flange will leak. Most often, a bowl rocks front to back, perpendicular to a line drawn through the bolts that anchor the toilet to the floor. A shim or two in the right place can correct the problem, but moisture will eventually cause wood shims to rot. Plastic shims are the ticket, and chances are you’v got some excellent ones in your picnic basket: plastic knives. The wedge-shaped profile of their blades makes them excellent shims.
As shown in the drawing, I use the wedge shape with the narrow edge pointing in. More than one knife may be needed. Take care not to go past the bearing point of the toilet bowl, and don’t drive the wedge in too tight; you could crack the bowl at the bolts or flange. Trim the wedges flush with the toilet’s base, and then finish the fix with a line of caulk.
Lance Bent , Baltimore, MD