I would recommend a back pack over buying a trolley system because for one, it's much cheaper, lighter and just as efficient. Ok, you have to pour the barrels but you get used to it. If you were to buy a ready built trolley system it will be relatively expensive, on the heavy side and with very little advantage over the latest back packs.
Big Boy back pack
The latest back packs are for instance 22 litre capacity which is not far off using a 25ltr barrel anyway. It has a flow of 4ltrs a min with 100psi. Enough to cope with anything you can throw at it.
All you need is one of these sack trucks which are cheap, light and collapsible. Then two or three bungees to hold the back pack on with. The back pack incidentally is the "Big Boy" back pack from Window cleaning warehouse. It even has a flow controller and battery condition display. It's the one I use every day.
Window cleaning warehouse also do special packages so you can buy everything together if you like so you will get just about everything you need to get going except for the sack truck which you can get on ebay or Amazon for around £25 - £30.
At first you might use more water and run out of water too quickly but once you learn how to conserve water and get those windows clean, then its really surprising at just how much work you can do with little water and yet have a good rinse. I often do downstairs trad still but increasingly, I am able to do the bottoms as well with just a back pack and I work fast. Really the secret is saving water by using at tap - but not just using a tap, its using it efficiently. There are a lot of them on the market now some better than others.
The only snag with all this is the water purification. If you live in a hard water area it will be expensive to buy the correct water purification system that will work efficently and economically.
Those lucky enough to live in area's where the water comes in at around 100ppm tds will be able to use a Di which is easy and relatively cheap to buy but this is a whole subject on its own. For an average day you will need about 6 25ltr barrels but I often use just 4 or 5 a day and do more work than you would think.
