If you can let the silicone dry out for 48 hours, then rins well with just water, including your tank.
I think you've got the small bricks (appr. 10 x 10 cm) thesegive appr. 1/2 a gallon of substrate when moistend. I always use hot boiled water to moisten the coco bricks. I find they pulverize easyer that way and let them set for a few hours. You can prepare them now if you want in a clean bucket, that hasn(t been used with any detergents or other chemicals.

Have fun.