Now then, thinking of adding some sill tanks, I could do with a bit of extra juice without filling the back with jerrycans.

Making them is no problem but how are they normally filled?

Thinking maybe poke some inch pipes up into the footwells with caps on, might be a bit messy though. Or maybe some flexible filler necks let up into the wings somehow?

Any clever ideas?

Could you pipe them in to the existing tank. Or via the fill pipe.

Left tank is connected to the filler, then connected to the right tank via a tube. Then a few T's in the existing lines. And it's all plumbed in. Simples.