Alan et al,
We've used the Whale Aquasource for the past 2 years on our Wyoming without any problems and it does allow you to dispose of the Aqua roll if that's what you're specifically after.
We simply connect one end to the full service pitch tap (the kit contains various adaptors for differing taps) and the other end, which contains the pressure reducing valve fits into the side of the van in the same way as the hose from the Aqua roll.
The onboard system is likely to be different on your van Ian, but on the Wyoming we have 2 levers which control the direction of water flow ie;- aqua roll to onboard tank, onboard tank to taps or aqua roll to taps.
Using the Aqua source, we set the levers in the 'Aqua roll to taps' position, which then provides an immediate and constant supply of correct pressure water, every time a tap is opened.
If the pressure reduction valve ever failed, I have been assured that the connector is designed to dump the incoming water on the mains connection side ie;- before it enters the van, so the van should never get soaked as a result of excessive pressure failure.
However, as a fail safe, we got in to the habit of turning the pitch tap off if we were going out for the day, this was after a neighbour kindly turned our tap off while we were out, after an errant mongrel off it's lead managed to chew through the pipe alongside our van.
This was the same mongrel who's owners tethered it up on the vacant pitch alongside us and allowed it to do it's 'runny' biz there on a morning whilst I was breakfasting....I can still smell it now, but don't get me started on that subject or the current "Anti Kid's" thread will pale into insignificance!
Either of the mains systems would fail under such chewing conditions.
Hope you get sorted,
Ken.