Hi noahjano,
Welcome!
I'm not sure what model year your T-2670 SR is, but in this case, it may not matter. Sunline usually only supplied one freshwater tank. Your picture under the bunk is your fresh tank. So, you only have one fresh tank.
As to whether a fresh tank is located under your camper, in your case, no, Sunline typically mounts the fresh tank either inside the camper or underneath it, depending on the floor plan and model year. As the years passed, older models of the same camper had the tank inside, while later models had it located under the camper as other design updates were implemented. This all depends on the floor plan and where the tank can be placed. Sometimes, it has to be placed under the camper, as the floor plan and cabinets cannot fit inside.
The other pictures you show, with the two white tubes sticking out of the bottom of the camper, are what they call low-point drains. Inside the camper, above those two pipes, there would be a valve on each pipe, one for the hot water piping and one for the cold water piping on the floor. Look in a lower cabinet; that's where they're most often mounted. By opening those valves and then opening the faucet to let air in, the water can flow out more easily, allowing a large amount of water to be drained onto the ground when you want to drain the water from the freshwater piping system. I say a large amount, as only about 60-70% of the water in the pipes will drain out by gravity. Pending the floor plan, the fresh water pipes run up and down throughout the camper, and not all the water will drain by gravity on its own.
I hope this helps, and I wish you a great time with your camper. We are here to help.
John
PS. Great pics! These help greatly show us what you are talking about.