A portable toilet carries waste to a holding tank, not a sewer. You add chemicals to control smell.
Portable toilets and camping toilets are designed for both peeing and pooping. Using kitty litter can help with odor, but ensure you have bags to dispose of waste properly. Air fresheners and cleaning tablets also help with smell. Open the door regularly to ventilate.
When the tank is full, empty it at authorized disposal points. Avoid leaving waste out in the open. Seal waste in designated bags then throw away or bury deep in the forest.
For urgent situations when camping, try lying down or standing to make it harder to poop. Holding it too long can cause health issues.