Sue, further to what Bristte said, look at - Click-On Hose Fittings - the top one is what the incompetents palmed off to you, the bottom three are the type you require.
The HP inlet on my van is this one - SHURflo Water Inlet with Mains Pressure Regulator - I have the right angle fitting permanently hanging out of it. That fitting has travelled there for well over 10 years without any problems. I have travelled a lot of gavel roads with it there and only had to replace the "O"ring a couple of times. the 'plastic' fittings are quite robust and suitable for leaving in place on your van
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PeterD Nissan Navara D23 diesel auto, Spaceland pop-top Retired radio and electronics technician. NSW Central Coast.
Further to what PeterD said, I also bought a batch of them from Amazon, which was very economical. Only a few dollars each when bought in a batch of eight. I carry them with me so that I can donate them to those on the road I meet who are in need.
I was at RTM recently and thought I saw a US-threaded adaptor, but when I went to check on the website so that I could give the link I could only see BSP ones, so perhaps I was mistaken.