I'm in the same boat.
the problem with Guzle's ones is that they are from the US and have an extra connector called city water which you somehow have to block off.
I got one about a year ago and managed to block it for a time but then it leaked again.
And guess what.......whilst trying to fix it I broke it.....
the problem with the c/w connector id that I think the thread being US is af and not metric.........
bet that's confused you.........
Sorry I had better add to that, the problem with the c/w connection is that unless its blocked, when you turn the tap and the water is pumped from the w/tank it just pours out of the c/w connector.
look carefully on Gunzles site and you will see the extra connector.
Rob.