Just to follow on.
Hire company loaned me the machine for free for the weekend to get used to it. The actual job doesn't start til mid August.
So i have had a bit of a play today, although not through a mossy.
The vac is a twin motor (don't do triple unfortunately) and I had about 4 metres of hose on it. I didnt seem to lose much if any suction, so gonna go with about 10 metres for the job.
Would a double motor be capable of keeping up with a mossy with vac port? Even if it sucks up 70% of the water i would be happy.
The dumping side of the vac i am going to put straight down a manhole.
Finally, is there an easier way of doing this, the vac has a 90L capacity, so I would have to empty it every 5 or so minutes, so on a big job this is going to take an age. There are some parts of the job i can get away with not relying on the vac so will save time there. But is there another method that would not require stopping every 5 minutes? I understand how a vac works and you cant defy physics.