Congrats on your new Sunny!
What model year do you have?
Over the years, Sunline changes the type of valves they used, called low point drains and the water heater bypass valves. The concept on what they do is the same, but how the valves is open/closed changes. Some you pull, some you turn to open/close.
I have pictures of the new turning types of valves.
For the water heater, you will need to find your way into the back of the heater. I "think" the water heater on the T2553 may be in the left (non door side) rear corner of the camper in the bedroom.
You might be able to see it from the rear cargo storage area and or lifting the bed up. These pics are from a different floor plan, (2004 T2499) but the water heater would look similar to most newer ones. There are 2 types of bypass valve setup's, the single bottom valve and top check valve is common. These pics are of the single valve setup.
At the bottom of the water heater, is quarter turn valve which is called the water heater bypass valve. The yellow arrow is pointing to it. That valve will turn 90 degrees, a quarter of a turn. When the lever is horizontal, that is normal operation and it allows water to flow into the water heater. Cold water goes in the bottom of the heater.
When the lever points vertical, that is water heater bypass operation and it prevents water from entering the bottom of the water heater. The valve then diverts water or anti-freeze up the vertical pipe between the top and bottom pipes.
On top of the water heater is another set of pipes and a brass fitting that screws into the top of the tank. That brass fitting is a check valve, an when it works correctly (they do not always shut off), water will not flow backwards into the top of the water heater but allow water from inside the water heater to flow out.
When you flip the bottom valve to bypass mode, water or antifreeze bypasses the water heater, flows up the vertical pipe, stops at the water heater due to the top check valve, and then allows water/antifreeze to flow to the hot water faucets.
Low point drains.
These drains help allow a large amount of the water in your camper piping to drain out onto the ground when opened. These help when winterizing the camper as you can drain the water line of a lot of water. Find your low point drains. They change location pending the camper floor plan, but most are on the floor inside a cabinet, bath, kitchen or water pump area. There are a few configurations of these 2 valves, but there is one hot and one cold. See here under the bathroom sink cabinet in a 2005 T-264SR
HINT! Before you turn those valves, mark which way the lever is pointing for normal operation. It is very easy to forget and get the directions mixed up.
To drain the piping, with the water pump off, open all faucets to allow air to flow into the water lines and break the vacuum in the pipes during draining. Open both the hot and cold low point drain valves and allow the water to gravity drain out. If you look under the camper for two tubes sticking down, that is where the water will come out. Close the valves when you are done draining.
Also, remove the plug on the water heater to let the water out of it. Since you are winterizing, you can do this first in the draining process. Leave the plug out all winter, and leave the faucets open all winter after you have pumped the anti-freeze through the system.
Hope this helps.