If you have a camper trailer with an onboard water tank, you may already have a pressure pump onboard. If you do have a pump, make sure it can provide anywhere from 6-12 LPM (litres per minute) and you'll be fine.
Then it's a matter of connecting your existing pump to the HOTTAP and you're good to go!
If you don't have a pump however, then you're best bet is to get the HOTTAP OUTING, which includes a 12V pump kit to be able to take water from the tank and push it through the HOTTAP.
You won't be able to just connect the HOTTAP to the water tank, as gravity won't provide enough pressure to get water flowing properly through the HOTTAP - that's why you always need pressurised water - either water from a garden tap at home, or a 12V pump if you're free camping.