This is the only time you should be cleaning the gravel. Once your gravel is in the tank, you should only vacuum it. Gravel hosts a lot of good, helpful bacteria that are beneficial for your aquarium. Rinsing your gravel will get rid of that bacteria. Store-bought gravel must be cleaned. It often contains dust and dirt that can be harmful to your fish. If you picked your gravel up from elsewhere, you will want to clean it as well. The smaller your gravel is, the tighter the weave you will need. Make sure that you are not using this colander or strainer for any other purpose. Also, make sure that the colander/strainer never came into contact with soap or other detergents. If you are cleaning sand, consider using a piece of cotton instead. If you have a lot of gravel to clean, you may need to work in smaller batches. The gravel should enough room in the colander/strainer to move around without spilling over the edges. Use a warm or hot water setting. This will help kill any bacteria. Do 'not add any soap, detergent, or bleach. Doing so can kill your fish. Shake and jiggle the colander/strainer. Stick your hand into the gravel, and sift it about. Keep doing this until the water runs clear. Turn off the water and give the colander/strainer a final shake to get rid of any excess water. Spread the gravel along the bottom of your tank. If you still have more gravel to add, repeat the whole cleaning process for each batch.

TL;DR in Indonesian:
Kerikil hanya boleh dibersihkan sebelum pertama kali akan dimasukkan ke akuarium. Buka tas pembungkus kerikil Anda. Siapkan saringan atau ayakan. Isi ayakan atau saringan dengan kerikil. Letakkan saringan/ayakan ke dalam wastafel dan nyalakan air. Gerakkan kerikil sampai airnya jernih. Pindahkan kerikil ke akuarium.