I had put the tank halfway along the end wall of the house. This meant it was at the top of the fall in the gutters, and although the gutters fell 10mm, the whole soffit of the house is curved up in the middle another 10mm. So we had 20mm of water in the gutters after I sealed the downpipes over.
The problem that arose was that the long side of the house has a dip in the gutter, so in the thunderstorm water poured over the edge of the gutter right outside the back door. This I didn't like, so I needed to get that corner downpipe working again. I decided to put a flap valve in the downpipe so I could direct water either to the tank or down the pipe to the drain.
After a lot if thinking I stood on the top of the ladder and cut the side out of the downpipe.

Then I drilled a couple of holes for an axle

I made a plastic mockup of the flap and then copied it in aluminium. The axle was actually a cutdown concrete bolt!

Drilling it was a trick. No vice or drill press, so I laid it in the join of the wooden bench with a lump of steel on it to hold it there, and drilled 2mm pilot holes by hand. The Ramset nail is my centerpunch! :lol:
I put the little bolts through and glued the nuts onto the axle to make them captive nuts, as I cant get at them inside the downpipe!

Putting it together means I can send water over to the tank-

or straight down the drain-

Then the route to the tank... my 6M of downpipe with a fancy flexible end didn't reach, so I reverted to making a straight joint into an angled one and then I could run a d'pipe straight into the tank. This was more highschool trig to work out how much to cut out of the joint for an 8degree bend, drop it in boiling water and glue it closed!!

This is how it all ended up! Now I just need to wait for rain to see if it works!