I think pyODK is a good way here (probably for all of your workflow) as it has some functions to make entity management more straight-forward:
You can do this by creating a csv (on your PC) with all the entities that you wish to delete (e.g. download the Entity List from Central). Then run a loop to provide pyODK with the uuid for each entity that needs to be deleted (this is stored in central as __id).
Take a look at the example for creating entities:
Then adapt it for the delete function...
OR
You could adapt the script from Bulk delete (and restore) submissions on ODK Central using pyODK to use the endpoint suggested by @danbjoseph - I think this is more complex (my script!)
I think at the moment there is no function to delete an Entity List, but I believe that it is in progress - this would be 'too easy' 
My advice would to become familiar with managing submissions and Entities through pyODK (or ruODK if you already work with R) - working at scale of 75k+ will give you a big headache otherwise. And if you go to data a collection phase without these tools, it will hurt. A friend told me...
If you are working with geometry based entities, check out QuODK as it might help (assuming that you are familiar with QGIS!).
Other tools are available, and there are still gaps in functionality for that specific 'recipe' I describe above. But it will get you closer.
I know that this is not a 'cut and paste' answer, but it is a fishing rod, rather than a fish... Good luck.