Yes a total of 8 tanks, 4 in each hull

Now the thing about building a catamaran, well there is pretty much 2 of everything, this can be both a good and a bad thing, the good thing is that if something breaks down - the chances are that the bit in the other hull will stay un-broken down, at least until the broken one can be fixed. The downside of course is that you have to buy, build and install 2 of everything. Having said that - I decided that I would have 2 totally independent tank systems in each hull. Each hull has 2 drinking water tanks, about 200 litres, black waste, grey waste (150 litres each) and fuel about 450 litres. A pump is mounted under the floor close to the tanks for pump out purposes. I also have a waste pump out point to the deck, not that I have seen any of these in Western Australia but I am guessing they exist somewhere.

Pumps

I have a bit of a mixture of Pumps, a pair of Jabsco drinking water pressure pumps. A pair of Whale Gulper grey waste pumps, the 320 model, had the 220 on the last boat and they were a bit slow but faultless. Black waste is handled by 2 Jabsco Macerator pumps. I will be carrying a spare fresh water pump, just because I have one.
I have a deck wash pump mounted below the rear steps on the starboard side.

WaterMaker

Although not really part of the tanks and pump section, well could not decide where else to put this and thought it worth a mention. I have a Spectra 200 water maker that is 200 gallons a day, or about 35 litres an hour I think, it is the base model without the MPC digital controller. I choose the Spectra because of good reports and the fact that the power requirements seemed to be close to half of what other makes required