Water pump for newbies

I have some newbie questions regarding the water pump.

I am taking my 177 out in 2 weeks for really the first time with hookups. The one and only time I took it out, I only had electric and used bottled water.

I had it winterized after that trip and the shop told me to just run the water for 5 minutes or so to run all the antifreeze out.
When I purchased the RPod I didn't get a lot of info-- and now I need to know how the water pump works.

• Do I only use it if I'm pulling from the freshwater tank?
• Or do I use it when I'm hooked up to an external water supply. In a nutshell, what does the water pump actually do (so I don't break something!)? 
• And if I'm on external water, I can leave my fresh tank empty, right?

And is RV antifreeze dangerous while I'm on the topic? What if there is leftovers that isn't completely flushed out through the pipes?

Thanks so much!!!!

Awesome. thanks!

Guess I am very fussy about the water I drink, but after the first year of owning our 2011  177 and winterizing with the RV antifreeze, it took me 3 attempts using different concoctions to rid the tank of that smell and have water that was enjoyable to taste. 

Ever since then I have hooked up my compressor for about 30 seconds to blow out the water lines.  No more RV antifreeze, except for the 2 sinks and 1 shower trap (about 1 pint) and now I can enjoy my sweet tasting well water to my hearts content w/o any foul smell or taste.

The only time I ever used RV antifreeze on our pod was October 2011.  The following spring I used bleach overnight in the tank but still had the taste/smell of antifreeze.  After that I used a mixture of white vinegar and lemon lime concentrate then filled the tank up, let sit for 24 hours and drain.  After that the tank was clean, no more smell or funny after taste.

My first mistake was to use a 2% bleach solution which only compounded my problem.  After that fiasco I used 1 gallon of white vinegar and 1 quart of real-lemon concentrate then filled my tank and let it sit overnight then the next day ran the entire 30 gallons through the hot/cold lines on both sinks.  Fortunately I didn't run RV or bleach through the hot water heater, already had closed the bypass.  Even after this I could still get a hint of both antifreeze and bleach so I repeated the process a second time with the white vinegar and lemon concentrate except this time I only added 5 gallons of water to the tank.  Let it sit overnight and ran the water lines for about a couple minutes and let it sit another day.  The next day everything was run through the hot/cold lines until the tank was empty.  FINALLY, the taste and smell were gone.  Have used air to purge the lines ever since w/o any leak issues.  A friend of ours had a similar problem with their RV having used antifreeze so in their case we just put in 1 gallon of white vinegar and 1 quart of lemon concentrate and added 5 gallons of water to the tank.  Let sit overnight and ran the lines for a minute and then shut the valves and let the mix sit in the lines for another day.  Ran the remaining mix through the lines and the problem was resolved.