Hello !
My darkroom is *also* in a basement. The sewer pipe is beyond a large concrete wall and about one meter and a half above the darkroom ceiling.
So i should have needed the bucket system for sewer ... But when you have a big bucket, one can put into it an electric pump, the king used for drain flooded basement. And put PVC pressure pipe to go to the sewer. Mine can push the water 10 m high and 50 m long. More than enough to reach the sewer pipe. Last but not least, you can use small diameter PVC pipe which make routing and piercing concrete walls easy. Mine use 25 mm diameter tubing.
The pump looks like this one : http://www.manutan.fr/pompes-vide-ca...MDL1772-9.html the blue round pad is the automatic switch (when the water level make this float, the pump turns on). Make sure you have a pump designed for acidic water or rince the bucket twice with clean water in order to prevent rusting and seizure.