Cleaned a pub last night with my boxer 427 fair enough didnt leave till 7 this morning but used 150 gl, the pub came to £488 twin tools one on upholstery (mining) and me on carpet (seen more hair and pile on a biscuit)
The new T/M's are the way to go with the exhaust diverter, ive a 80 gl tank can get three, 3 bed houses from that if im realy lucky but i recon thats good, then connect to stand pipes £50 a year and as much water as you want or from
Connect to any tap upstairs or down, even been known to connect to next doors 
explain that 80 gl is going to cost them about 23 pence thay dont mind
