Leaving it to the buyer to supply the short connection pieces is not your best plan. Small sections of pipe in the relevant size are not sold independently so we are left to beg off-cuts from agents.
Once assembled the location of the unit is an issue as the application of the system is to repove debris and dirty water which will be destined to a storage tank. The system requires a vertical section of no less than 45cm, which given that a 5000 litre tank is fairly close to the lower edge of the gutter, this is unlikely and in my case impossible: particularly since there are 2 tanks and the joining connection complicates this even more.
