Just in case about the filler.
The kitten can use anything - a net, toilet, etc. But everything must be done gradually and smoothly. First you need the filler he knows.
We had a case where (despite all the reminders) a kitten was given a tray with a net without filler. He started writing everywhere in the house. It's nonsense for us - we have since the month all the iron go where it is necessary. I began to find out that there was no filler. I feel sorry for the kitten in this story. I went to a new house where the toilet was not clear. He endured 2 weeks "to the last", and then wrote in the nearest secluded place.
Don't do that, pity the belly. If you want a mesh - well, pour the filler on the mesh and gradually reduce the amount.
If you want to go to the toilet - buy a nozzle on it, sprinkle with filler and gradually increase the hole. We practically trained Visik to do that. She figured it out. And when Laska arrived, there was a problem - they always had to go to the toilet at the same time. Just the two of us together. "we came to write in herd." They didn't fit together. Then we spit and went back to the trays. That was the right thing to do, because then the kittens went