hrm...
The carts currently fill up with liquid when they are in a liquid square.
Are there plans to attach pond filling to cart-available actions?
Put a loop of rail in to connect a cistern with a rail line running through it with a pond you want to keep full? Allow the cart to move through the water to fill, then dump water in the pond?
Can this be implemented with Magma for Magma ponds? *grin*
So how do we think dumping/removal of liquids in carts could be handled?
My initial thoughts are of a constructed (but not powered) tile with a mechanism that tips the cart without stopping it, emptying it's contents in a direction. This would allow automated filling of ponds/magma ponds and seems pretty intuitive. It could also work with the brake tile, so you could have a "stop and dump" action, but then you would have to get the cart started again.*
Of course an alternative is manual/dwarf labour action to empty a cart in a location. This is a neater option for carts that have been accidentally filled, to avoid a situation where, like buckets, they cannot be used for other purposes until emptied. Although this makes me think of dwarves scooping magma out of a cart with their hands.
*Which is another area i'm unclear as to how it's going to work, do dwarves have to manually push a cart stopped on a brake tile? I know they are not combined brake/booster tiles, but can, for instance, other carts jump-start a stopped cart? Or does simply releasing the brake let the cart on it's way?