Duetto Water issues

A friend of mine has just bought an 05 Duetto.  When she turns the water pump on, water squirts out of a black rubber pipe under the floor behind the water tank. I presume this is a frost drain, but we couldn't find a tap inside the van, and couldn't work out where the pump is anyway.
Also, she has no electric flush working on the toilet, presumably, this is fused somewhere?
Thanks for any help you can give.

Some vans have separate toilet water pumps in the toilets water tank and this sometimes has a fuse, as described, but often, after a period of non use, the pump sticks and won't work. The way to remedy that is to remove the pump from the cistern and twiddle the central metal rod. This usually frees it off and it works fine. 

If the Duetto has no separate toilet water tank, it will be fed and pumped by the  van's fresh water tank, using the van's pump.

I'm a tad concerned at the OP's description of the initial problem. Any drain vent shouldn't need the pump operating for it to drop water. A pump system works on building pressure in the pipes and the pump turns off when a set pressure is achieved and turns on again when the pressure drops e.g when a tap is opened. If a pump is continuing to work and pushing water out somewhere then you have a leak. It may be a vent, but that should leak water whether the pump is running or not.

Dave, 
Does the Duetto have a separate fillable water tank for the toilet, or is it fed from the fresh water tank?

Hers has a separate tank, I'll check the fuse. Good point about the drain pipe only working when the pumps running.

Some Thetties don't have a fuse in the cassette locker, so if it can't be found, don't worry. I'd emphasise that the stuck pump, that just needs a quick twiddle is the most prevalent problem. Details of how to access the pump are shown in videos on the Thetford website as are useful parts diagrams for each model.
The pumps stick through lack of use when dry over winter and if on dealer forecourt etc