I've had some luck using a flat head screwdriver to check if there is any silicone left. I have everything done but the 4 corners on the bottom. I don't know how to get the silicone out of those.
I would wait seven days for the silicone to cure properly before you water test it.
Silicone takes a while to cure properly all the way through, it may seem cured when you touch it after 24 hours but underneath it will still be wet.
Clown loachs need a much bigger tank as adults and imo they don't mix well with active cichlids.