Feed them choped up protein food,i use Blatta lateralis and i cut the bottom half of the body and slightly squish it so the juices come out,and i remove out the brown/black fecies because i think they wont eat it,it looks complicated but if you want to sucseed at feeding trust me. When they are small they even cant eat a roach if it isnt cut up they just leave it to rot. When they are finished after 2 days just remove it with a ear stick and clean it a little bit with the other part of the ear stick that is soaked in water and give them a freshly cut bottom half of a roach
That is how i do it and it is clean and they eat the juices