Water tank Help

[K&S"]

Hi. We’re heading off on our first camping trip tomorrow and have yet to fill the water tank. We’re going give it a clean today but have no idea how much we will need for a couple of days away. Don’t wait until arrival at the I met a couple who had a camper (transporter) and they said they never use the water tank at all. Do you use it for making tea/coffee etc or just for washing up? I will take bottled water for general water drinking.
We’re looking forward to staying in the Cali, bought way too much stuff but we’ve no idea what we will need until we try it out, but windy weather on the way may not make it the best

 

[secret lemonade drinker]

If you aren't going to use the installed water system in an Ocean why didn't you buy a Beach?

 

[sticky1]

You’ve motivated me to stick the scope in the tank and see if all the water drains out when you open the tap. If the pump is mounted at the bottom I’m hopeful it fully drains out.

For those that are interested this is the bottom of the water tank - I now understand how it works.
The tube at the back looks like it’s a plunger, so when you open the tap at the top it raises the plunger and drains the tank. Which gives me confidence that when you empty the tank it fully empties.
Second image is the submersible pump. Which I think shows that you need to run the tap until it runs dry as the pump seems to pump up and along to the tap.