Silicone removal

I am replacing two panes that broke in my 29gal tank... the bottom and a short side. I've got the new glass and silicone ready to go.
I've just gotten the last chunk of broken glass off and have been taking a razor blade to the silicone remaining on the edges. Even when i think it is all gone, I am seeing a slight film. Is there anything that will remove this last bit? I'm assuming I want the surface absolutely free of the old material so the new layer will adhere and seal well when I place the new panes in place.

Also, when I do get everything put back together, how long should I let it cure before testing my seal? And before filling it again with my nice aged water? I don't want to contaminate that and have to start from scratch.

Thanks.

Actually old water from the tank it will be replacing... doing a bit of musical tanks to rotate fish between two old tanks and ultimately into the one as I'm not going to have room for multiple tanks for a while again.

Thanks to both of you. I should have some of each hiding around here somewhere. It will be good to get my "big" tank back in operation for more than a home (long ago) for rats.