definitely an issue below the capping station. if disway wash doesn't drain it, it can be anything from a clog in the line to your new pump already being a bad pump.
I've had a new Triangle pump fail after just 2 weeks of printing, the line split within the mechanism and ink dripped out until it clogged up entirely.
anyhow, for your fix:
0) overflowing waste container?, possibly clogging or submerging of the black drain line and discouraging the normal flow of the waste ink.
1) clogged capping station? make sure capping station is clean. drain the black ink with a paper towel or swabs, remove the metal screen, and rubber cap, and clean thoroughly.
possibly even disassemble capping station to clean the white plastic cap below the black rubber sealing cap. *be careful that, if you do so, there are springs beneath the capping station cover that will get lost inside your printer if not careful.
2) clogged capping station-to-pump line? open up the backside of your printer, and examine the lines that go from the capping station to the pump. I believe there is a second cover that you'll need to remove, as well, to get a better view. if there are any clogs, then disconnect/clean/reconnect. If you can't tell, then run the disway wash, and go back around to the pumps and observe. you can better see where the error is at this point.
3) clogged drainage-lines? check your drainage lines for clogs
4) if no clogs above or below the pump, then diagnose the pump:
-swap the black line with the yellow line. there's a metal piece that joins the capping station line to the pump line, just seperate/swap. disway should now drain the black line. This is not a fix, as now your yellow line will most likely be acting the same way as the black has been.
5) if none of the above worked, now you'll now have 1 of 2 solutions
A) needs new pump
B) new pump was improperly installed, and would require removal & advance the gear mechanism a few steps, reinstall and repeat until disway fills/drains as it should.
explained: the pump operates by essentially rolling a "straw" (ink line) from one end to the other, and encouraging the siphon effect of the ink system. two lines ("straws") per pump, operated by 1 gear and a rolling mechanism for each line. half a rotation of the pump "opens" the line and the other half "closes" the line. if the gear is a quarter of a rotation off, it could easily leave your Magenta open but the Black closed(or visa versa) when it is supposed to leave both closed, awaiting it to open/close again and again when the pump is engaged.
best of luck!
once you've found for fix, make sure you do a LOT OF CLEANING or your printer will be mad at you. de-gunk the sides of the printheads, replace wiper blade, disway wash a few times, run a long nozzle wash...and close the cover with your fingers crossed, before spinning around three times and clicking your heels together while repeating "MikePro Rules".
...and up your scheduled cleanings. disway wash should be a weekly routine.