Leaking tank

This is my first post here and I'm scratching my head over the problem I'm having. I bought a Gerber Avalanche RF on Friday. Installation was a breeze....easiest I've ever had. The problem.....the tank leaks at the flush valve outlet to the toilet. It has a Fluidmaster 400 Anti Siphon 3" valve that was preinstalled. Prior to installing the tank to the toilet, I checked the plastic retaining nut for tightness and found it to be secure. I placed the large bevel washer correctly, hooked up the water supply tube and filled the tank and checked for leaks...none found. The toilet flushes fine. I left the area for about 2 hours and went back to check for leaks and found a puddle of water on the floor. It was wet between the tank and the toilet, however there was no leaking from either of the tank retaining bolts.
I drained the tank and removed it from the toilet. The area around the nut and bevel washer was wet. I then placed the tank on a stand so I could observe the bottom of the tank. I rechecked the tightness of the retaining nut for the valve and filled the tank to the water level. After a few minutes, I found there was water weeping from between the plastic retaining nut and the bottom of the tank.
I drained the tank, removed the valve from the tank and checked it for cracks and also the soft gasket at the bottom of the valve for damage. Everything looked good. I placed the valve back in the tank, tightened the valve retaining nut (making sure I didn't overtighten it). I then repeated the test on the stand. I let it set for about an hour and didn't see any weeping. Basically, it felt dry to the touch.
I then reassembled the tank to the toilet only to have another puddle on the floor after about an hour or so.
Does anyone have any suggestions?? I'm not a profession plumber, but I've installed many toilets over my 63 years and have never had this problem. Thanks in advance for any help.

Take the valve out, take some emery cloth or fine sandpaper and smooth down the area around the seal, wipe it off, then reassembly. You can do this around the tank to bowl bolts, too.

Thanks for the quick reply. I'll try that and post back with the results. Thanks again.

Well, I did the emery cloth proceedure.....about an hour and 1/2 later, a puddle on the floor and the area between the tank bowl and toilet is wet. Also, the large bevel washer between the tank and toilet is also wet. Is it possible that I have a defective tank/valve????

I'm going to say you may have a defective tank.
I would return it and get another.
For what you paid you shouldn't be having problems.

I would also ask that you post a review of your experience at this linked thread.
https://terrylove.com/forums/showthread.php?p=119444#post119444
There really are not a lot of postings on this toilet and your experience would be good to share with others.

Thanks Redwood. That is the conclusion that I've come to also. I will be taking the tank back to the plumbing supply house tomorrow. Will post back here with the results and a recap on the link you provided.

Problem lead solved

Well, I returned the tank and everything that came with it this morning. The plumbing supply house where I bought it asked several questions about my installation proceedure and agreed to swap out the tank with a new one. I returned home, installed the tank and filled it. A little over an hour later, I checked it for leaks and found it to be completely dry. I went to work and upon returning home about 5 hours later, it was still dry as a bone. Problem solved. Thanks for the help and advice.

Well glad you got it done okay. sorry you had to do it twice...