Shout out to Princess BenKun
for finding out that you only need to do Wave 50 (or 25 if you want to go the other route, I only cover 50 in this guide).
Map: Blood Drive
-Precision Rifle Damage
-Precision Rifle Capacity
-Sniper Strike (you can swap this out for something else)
All my skills were at least level 5, higher will obviously be better but this is still very doable. Lower skill cards might be able to do it but it might take you a bit longer.
Watch this video:
That person is playing on a harder difficulty so that just means we can get more wiggle room for error.
Use the Fabricator to block the door. (If you have a hard time placing it, make sure you're outside of the spawn to push it in.)
Put down two Sentry Turrets facing the spawn area and then put three Decoys blocking the other door then put down the two floor spike traps the way you see them in the video.
Now wait to see if you got a Snatcher spawn, they should appear top of the stairs opposite the ones you're next to on the other side of the map. If it's not a Snatcher, die and check again.
Once you get the Snatcher run inside and hug the wall as shown in the video.
(If you decided to take Sniper Strike, you can get it off two or sometimes three times before the Snatcher comes. Be careful as it will insta-kill you at close range.)
Now just do as you see in the video, stay on that wall and watch for the occasional spawn inside the spawn area or the room with the Decoys blocking it. Move a Sentry Turret if needed.
Usually only two Snatchers spawn but if you kill them more quickly than the other enemies then you might get three.
Once you got a good run going, should take roughly five minutes to complete the wave. So if you account for the odd mess up or waiting for the right boss to spawn, this really shouldn't take more than thirty minutes to get the three waves done.