Boondocking and Water?

We have a 100 gal fresh water tank but only put in 20-30 gal in before leaving home . Most of the time we boondock its a long way from home and involves a stay at a campground closer to our final destination where we will boondock for a couple weeks or so. We fill at the last campground in those cases. We also carry a 20 gal foodgrade drum we got for 15 dollars from a local source that sells them. I bought a small transfer pump from harbor freight for less than 20 dollars and mounted it inside the bed of my truck and made a plug that will plug into my camper plug in the bed to power it.
If we boondock withing a day of home we just fill before we leave unless we know for sure of a place to fill closer.