That was my first time trying to derim a tank. This was my 5.5 gallon tank so i didnt really care if i messed up. Anyway, the rim of this tank was a plastic, its not wood by any mean. So you just gotta use blades or anything ( i used knife..) to get under it to trim the silicon. I recommend you to do a serious research otherwise you might get mad and cut your self like me ( a little on my finger but blooded quite lot).