He wants to set up a flushing machine to flush any goodies that get dropped to .... Will this work?
.... What could go wrong?
Just the flushing portion will be extremely difficult to make it both work and not be insanely annoying. There are two problems:
Problem 1. Flowing water moves objects, but "pressurized" water does not: There are two ways that water moves:
A. Flowing: this is where water moves from one square to an adjacent square with a lower water level. If you have a large wave of water, this only occurs on the leading edge. For example, if a hallway has 7777776421 water levels, flow only occurs on the front 5 squares. This means that once an area has filled to 7/7, no more water "flow" can happen and items won't move any more. This makes flushing items a long ways difficult, as you have to somehow meter the water to keep it from switching to the second mechanic:
B. Pressure: Water under pressure (from a pump or from falling from a higher level) does not "flow" the entire way to the lower water level. Instead, that unit of water finds a place with a lower water level and teleports to the new location, not affecting any squares in between. This is one reason why items stop moving once the water level is 7. The result is that high-pressure water traps don't move items nearly as much as you'd expect. (
http://dwarffortresswiki.org/index.php/DF2012:Pressure)
Problem 2: Items become invisible when moved by water flow:
http://www.bay12games.com/dwarves/mantisbt/view.php?id=895This one is maddening for this kind of project. Items will stop appearing on the map. They're still THERE, and will generate jobs as normal, but they won't appear when you loo'k' at the square. If a dwarf interacts with them, the item reappears. One thing you can do is 'd'esignate the area to claim and dump the invisible items, or find another way to get them queued to be picked up.
The result is that, maybe your carefully tuned water-flow item collector is working, and maybe it isn't, but you can't tell by looking!
My advice, having dumped an insane amount of real-life time into very similar projects, is to start with a VERY small area for your item flowing/moving/sorting project. After trying it in a 2x10 or 2x20 area, THEN decide if you really want to wrestle with the problem on a larger scale. After my self-cleaning goblin pressure wash project ran into these issues, I decided it just wasn't worth fighting the game mechanics and one prominent bug.