You've gotten some great responses here (it's actually a question that shows up with some regularity). You've got some decisions ahead, and need to consider what will be most important to you and your set up.
Much of what we're providing is information, though it seems like you're also looking for advice and a recommendation. Likewise, there's some thinking that I hope doesn't get lost:
1. You've got to decide if you want (a) your water to stay confined within the IBC container, or (b) if you want to migrate it to the fresh water tank (and how much you want to bring along). There are ways to do both, and advantages/disadvantages to both. Likewise, you can always travel to your site with your RV's fresh tank full, which would take a bit out of PART of the water supply question (I like to travel with dry tanks for reasons, and fill closer to my destination, but that's me).
2. Following #1 - and with no hookups - you've got to decide how you're going to (a) dump the waste tanks and (b) get rid of unused fresh water in the IBC and/or in the fresh tank. If the fresh water/field tank is full, you can either pump its contents into the waste tank(s) and get rid of it the same way you're getting rid of your waste, or dump it straight out using your rig's tank dump valve... but that migh drop a lot of water where you don't want it - directly under your RV.
3. Since you're not going to be permanently onsite (save for a week at a time over the course of two months), AND you don't have hookups to dump water easily, it sounds like the water supply (with 150gal) won't be the limiting factor, but your waste tankage will be (like it is for most of us). So you're going to have to solve for waste, and that might help you work backwards and decide how to best deal with water source.
4. You're either going to have to deal with waste by (a) dumping gray and black into a waste tote and moving that; (b) moving the trailer to a dump site; and/or (c) potentially a hybrid solution of using
a hose and hosecap to migrate your gray waste tank away from your campsite and dumping that on the ground safely (only if legal and viable in the state/on the property you will be on.
Texas does makes some provision for dumping graywater to ground.). This would help take one of the larger limiting factors (that of gray waste water) out of the equation. Now you've only to deal with the black tank, which will either need to be emptied to a tote, or emptied when you move your RV offsite to a proper disposal facility/dumpsite.
So, it you want to keep the water in the IBC rather than putting it into the field tank, though that will mean that the IBC will likely have to stay in your truck (since offloading a full 150 gal water tank can be a LOT of weight), and your truck close enough to the trailer to be able to draw from it. This means if you want to take your truck offsite, the water supply goes with it. Will there be a second vehicle there such that you can leave the IBC tank in the back of your truck and leave the truck in one spot for your week-long stay?
If you've decided that you want the water to stay in the IBC container, you have to decide if you want to use (a) an external pump (you'll go in through the city water supply, as it's usually tied in AFTER the onboard pump) or (b) the onboard port (and you'll go in through the antifreeze port - if your rig is equipped with one). If you're going this rout, I'd suggest that you go in through the antifreeze port, use the trailers internal pump, and simply run a fresh water hose to the IBC - then you don't have to worry about your external pump being (1) plugged in/connects and (2) set at an on-demand setting that your RV's plumbing can happily handle.
If you've decided you want to want to use the fresh water/field tank, you've got to get water from the IBC to the fresh tank.
Depending on your specific rig and plumbing setup, the simplest (and only guaranteed direct) way to get water into the fresh tank is via the gravity fill on the side of the rig. (Note: not all rigs are alike, there are some plumbing systems have a fresh water source to tank fill selection). There are also some workarounds (like (a) use of the showermiser, if equipped, to get water from the IBC to the fresh tank in through either the city water or antifreeze ports; or (b) use of an outdoor shower that can reach to the gravity fill; or (c) use a siphon with the IBC being higher than the gravid fill), but what's likely the easiest and most reliable for you would be to use your external pump to pump water from the IBC to the fresh tank via the gravity fill.
If you travel with a full fresh tank, you won't need to add any till later. But until you figure out how you're going to deal with waste, you don't have to worry about how to deal with fresh. Since waste tanks can be a limiting factor (and you might not have 150 gallons of combined waste storage), you probably ought to start there.
For what it's worth, I sorta like taking bits and pieces of the best aspects of solutions and building something that works for me.
Last thoughts:
1. Having 30amp power on site makes a big difference here. Means you can pump to your heart's content without worrying about impact on battery.
2. Love the use of the IBC container! (I assume you have
an IBC-to-garden hose cap). If filled to capacity, that's a lot of weight to have to deal with (can your tow vehicle handle this weight AND tow your trailer if going out in ONE trip?). If you can get the tank out of the truck and leave it onsite, your truck gets freed up and your site layout easier to manage. If you leave it in the back of a pickup truck, it might be high enough such that you can just siphon right into the fresh water tank via the side/gravity fill.
3. Lastly, what's your RV year/make/model (always helpful to be able to provide model-specific help from owners)?
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Sorry, this is a lot. I get pretty long-winded.
Executive Summary:
"How can I get water from the container to the RV? Do I pump it into the fresh water tank using an external pump?"
Yes, you can go IBC to gravity/side fill using an external pump. Depending on your setup, you may also be able to use the siphon method
"Can I use the RV pump to add water from container to the RV system going directly into the city water outlet?"
NO, if you go in through the city water outlet you need to use an
external pump. If you use this method, water won't go to the tank, but it will be available to the RV using pressure supplied by your external pump.
However, if you go in through the antifreeze inlet (if equipped), you CAN use the
onboard pump. If you use this method, water won't go to the tank, but it will be available to the RV using pressure supplied by your onboard pump.
There are some potential, indirect ways to use the onboard pump to get water into the fresh tank, but - if you have an external pump - you are likely better off using that to get water from the IBC to the fresh tank via the side fill port.
Lastly, dealing with waste will be an important consideration. If you have to move your trailer to dump, then you likely can fill the fresh tank at/near your selected dump site.
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Lastly, here's a non-specific, fairly common plumbing diagram for some FR towables. Might help you suss out a solution that works for you.
Just my .02. Hope this helps.
