I used a gun for mine and probably went through 3 and a half tubes but my tank has a 5'x3' footprint and has some extra glass wedges in each corner to help take the force of the water. so I had to use a little more silicone. And the other guy is right no matter how much you think you have got off there will always be more. wear gloves and eye protection too.
My step dad is a commercial oven repair man (sounds boring but he makes nearly $100k a year) and he had some really high quality waterproof non toxic silicone, did some reading up on the brand and checked and asked questions on here and determined it was safe to use. never had any problems with the process because I made absolutely 100% sure that I knew the next step before I went on.
It's actualyl a pretty fun little project and you feel rewarded afterwards, even if the room of the tank will stink like vinegar until the silicone is set
