My Toilet Diagram. The toilets drain size. Despite your plumbing code 3 inches is the minimum drain size for a toilet.
As the toilet flapper closes off the water to the bowl the toilet fill valve sometimes referred to as a ballcock begins to bring water back into the toilet tank to recharge for the next flush. If the toilet is a new addition or is being sited in a position that requires re positioning waste. Take the cistern lid and flip it over.
Look for the manufacturer name or a number on the bottom side of the water tank lid.
To fill the tank and to empty the tank. Here you can see the parts labelled. The silent fill valve and float system with labels. The most intimidating part of a toilet is inside the tank.