I amde the hole a little larger, and the sink moves side to side, and front and back, but will not go down. I sat it upside down on a pile of drywall, and it rocks. Does this mean that I have to try for another one? How bad is too bad? The counter top does have a small sag in it (like you described) when I put the level front to back, but I doubt that it's as much as the gap between the sink and the top. My rocking and big gap occurs near the bullnose face, and the pivot area is on both sides, about half way back. I can rotate the sucker around, move it side to side, or front and back, and nothing changes. I'm guessing that my hole is big enough - I really don't want to take anymore away. How well/bad should it fit?
Rodney
OK, I hope it doesn't move side-to-side or front and back very far.
Sounds like your sink is warped. I'd take the sink back to where you bought it and show them how it rocks on a flat surface. If it does that, then it's gotta be warped. A sink is made to fit properly on a FLAT counter top.
Normally, plastic laminate tops will curve concave UP from the front bullnose to the rear backsplash. I've been told that's because they heat the plastic laminate so that they can bend it to conform to the shape of the counter top. When the laminate cools, it develops tension, and that's why you might find some "cupping" in laminate counter tops. Your top seems to be bending the opposite way, OR your sink is warped, prolly the latter.
To locate your NEW sink properly in the hole, move it north, east, west and south, and mark the furthest extent of the sink in each of those directions. Then, position the sink in the middle of those marks and trace it's outline onto the laminate. What I do then is apply plumber's putty to the counter top between the edge of the hole and that line. Then I put a 5 gallon pail and a car's scizzor jack under the sink hole to support the sink just above the counter top. I'll have a helper lower the jack while I guide the sink down onto the marked outline. Then I know the sink is centered in the hole.
Personally, I would use plumber's putty instead of silicone to install the sink, but either one would work fine. Perhaps the best would be to use plumber's putty under the lip, and then caulk around the lip with silicone, depending on whether the lip is thick enough to do that. I say that because I'd be concerned that removing a sink that's siliconed down in future might prove to be a real fight. Silicone caulk sticks like crazy to porcelain.
See what the store says about the sink itself. From what you're saying, that sink is warped.