Kitty Litter Robot Funnel

We have one of these self-cleaning "robot" cat litter boxes for our 2 cats. It does a wonderful job of taking care of things, but it is tricky to fill with fresh litter. You press a button on the machine, it rotates and gives access to fill via a small 8cm x 8cm opening. Pouring the litter through this awkwardly small hole takes much concentration. I designed a funnel that fits into this opening to make filling it much easier.