A little tutorial for you
Welcome to the forum and RVing...don't be afraid to ask; we all had a humble beginning at one time
Your water pump will only draw from your fresh water tank
. The inlet pipe to the pump comes from the fresh water tank. The outlet pipe from the pump then joins the inlet pipe from the shore water connection. There is a check valve right where the shore water inlet pipe connects to the sidewall of your trailer (where the water hose screws on). This check valve prevents the water from your water pump from being pumped outside through that connection. It will only allow water into your trailer from the shore hose and will not pass water out of that connection. The water pump itself, acts as the check valve to prevent shore water from going into the freshwater tank. Water coming in from the shore connection cannot pass the water pump, that's how it "pressurizes" your system and water from the water pump can't pass outside through the one way valve and that's how it pressurizes your system. Two inputs, but, due to valving and the one-way nature of your pump, only one "out bound" direction for the water...your faucets or toilet
If you are going to a "full service" (hookups) type of campground and you hook up to shore water, there is no reason to have water in your freshwater tank or to ever your pump on. I never carried water in my freshwater tank (I don't "boondock"; the term used to reference RVing without water/electric hookups) and I never used my water pump except to purge water from its outlet pipe (it will fill up over time from the shore water pipe, but, it won't go past the pump) when winterizing.
As a "rule of thumb", you don't put anti-freeze (commonly referred to as "the pink stuff") into the water heater. You will play the devil trying to get it all out. The way the tanks are constructed, even pulling the anode, leaves some water or, in this case, the pink stuff in the bottom of the tank. That anti-freeze will dilute in the water next spring, but, it will take a while to get rid of it and some folks, like me, are "hyper sensitive" to the stuff. I don't like my water to smell or taste of the anti-freeze solution. Your trailer should have a water by-pass system (you found it) and you use that to take the water heater out of the system before pumping the pink stuff through the water pipes. To get the water out of the water heater (with the water still by-passed), you'll need a 1 1/16" socket to take the anode out (the anode is the big nut at the bottom edge of the tank; accessed through the outside panel that covers the water heater)...this should be done annually, at any rate, to check the condition of the anode and most of us do that in the fall when we winterize. When you take the anode out (stand to the side...6 gallons of water comes out pretty quick
) the water will empty the tank for you. What little water remains in the bottom of the tank, even when/if it freezes, won't cause any damage. While you've got the anode out, if you have a water heater flush wand, flush the "crud" out of the bottom of the water heater, if you don't have a wand, just use your garden hose sprayer to flush out the tank; you would be amazed, even when using a water filter on the water inlet, how much "crud" accumulates. Your anode should last for years, however, the annual inspection should cause you to replace it when it gets down to 1/4" anywhere on its length or if you notice a steel rod showing (the Zinc rod has a steel core); either of those two conditions mean that it is time to replace it to maintain its effectiveness. Some people leave the anode out to remind them to switch the by-pass valves back in the spring, but, I don't recommend that. If you leave that hole open in your water heater you may invite mice to move in...you definitely don't want that to happen. Put the anode back in...you'll need to take about 3 turns around the threads with white Teflon plumbing tape. Put it in snuggly, but, don't over do it; if you strip the threads you are really up the proverbial creek without the paddle
Look through this section of the forum...there are a couple of really insightful threads on winterizing; both with the "pink stuff" and how I do it (with air).