Having owned clown loaches for over 10 years, I know that there is no way they can remove all the snails. Loaches can help control the snail population, but not totally eliminate them.
Without having to totally tear down my tanks, I always see snails, even where the clown loaches reside. My other tanks, I constantly remove snails, at times, over 20 snails per day.
I would have to safely assume, for every snail you see, there are at least 2 elsewhere.
I'm not sure what the hatching lifetime of snail eggs, but I would have to think that to totally eliminate snails, run tank with all equipment, decor, rocks, etc with the tank full of water. So full that the water almost overflows from the tank then add allot of bleach. Run it for about a day or 2, drain the water, rinse everything, then will with water again to the top. Wait about a week or so, then add bleach again. This should eliminate any snails that hatch from eggs.