M = magma/water tile
xX = pump from west
ts = track stop, iron minecart, set to dump north (into a wall)
MxXts
That last line is a setup (powered from above and not detailed here) that I used to breach a magma shaft eleven z's below the volcano's top magma level. I had a dwarf channel directly into that shaft and they did so quite safely.
Meanwhile ten z's worth of lava drained down into my iron minecart and disappeared... yes, really.
Works with water as well.
As far as I can tell you can pump as much fluid onto that track stop as you want and the minecart will simply dump it into the wall to nowhere.
Properties:
The trackstop the wants to stay at 5/7 when the pump is pumping. Indeed, if a portable drain is setup in a large room, the PD will work to keep the entire room at 5/7.
The PD will drain a non pumped source... Say, you open a floor hatch from the bottom of your huge water tank... Properly setup the PD will drain that tank down to a single 5/7 tile of water. The PD will not drain as fast when fed this way. The pump/s force feed the PD, as fast as you can pump onto the PD. I set up four pumps to pump into a single PD tile. Each pump was fed from seven aquifer tiles. By counting the missing slices of water on pause, I was able to ballpark the rate of drainage at approximately 185 slices... At each pause..
A non pump fed PD drains at about two slices every fourteen ticks. (I tested a gravity fed PD at the bottom of a three tile vertical shaft. The shaft appears to drain faster at first so pressure might force feed the PD.)
The PD will not stop flow into open tiles, but as soon as the fluid has no place to go, the drain will destroy any further flow.
The track stop can be switched from "bottomless pit" mode to "fillable"
A water PD cannot accept magma. Each fluid must have it's own PD.
A pump can be used to dump fluids "directly" from the minecart. So a pump setup to pump from a tile that has a trackstop dumping into a wall, will empty the cart as it passes under the pump's feed hole.
The implications for flood prevention are obvious. Drowning chambers can now be designed without a recovery cycle.
Level of lava in volcanoes can be very easily controlled. Forts submerged in lava are easy to set up.
Lots of ways to use this gizmo.
Enjoy