I think he means that they use there own toilet seats when they go potty. So when going to the potty room, they carry along a toilet seat with them and when they enter a stall, they install the seat.When they are done, they remove it (and hopefully clean it) and return it to it's proper location.
I think seigewar wanted to know if they shared it "Hey, Todd, I'm going to the bathroom now, can I borrow your toilet seat?"
Can you imagine if things actually were like that? That would be unusual for modern society,