Hi Bonzer, water weighs 1kg per litre, so 500L = 500Kg, add to that a pump and battery and a di vessel, another 20-35 Kg depending on what size of battery you choose. The tank itself will weigh 5-10 Kg. The poles assuming you have a 18ft and a 30ft pole, there's another 10Kg. A hose and decent reel, get a good metal reel, another 5-10 Kg depending on whether its microbore or standard. A bucket and trad tools for the windows you cant do wfp, 5-10Kg. your lunchbox and flask (hopefully not a broken one!!!
), 5Kg. Some warning cones, another 5-10 Kg. And dont forget to add your own weight and also add the weight of a full tank of fuel, and have enough weight to carry a passenger too.
Maybe better to go for a 400L tank, I have a 350L tank and have not run out yet, worked a 7hr day and still had some left.
Tim