I know this doesn't bode well for this project but I''m rethinking the list of tasks in the previous post already, not so much the contents as the order.
It has occured to me that if I...
1) install the tanks
2) connect the first tank to the utility room drain pipe
the next time the washing machines are used the first tank fills with water so when I go to cut a hole in the tank to connect it to the second tank..... big flood and I probably electrocute myself with the drill.
1) install the two tanks
2) connect the two tanks together
3) run a pipe from the first tank to an old shower pump and then on to an outside tap on the wall
4) connect an overflow from the 2nd tank to the main sewer (via a u-bend)
5) connect the first tank to the utility room drain pipe.