How to erase your phone securely

Hello,

I know, there are dozens of threads, articles and recommendations over XDA and internet. But I am still not sure what best practice is. Erasing Hard Disks is quite easy. In this case one deletes the whole storage from an external device. One can also delete unused storage and so on...

However, I have not really any idea how to delete the storage of my phone, especially internal storage of my Nexus 5. If i plug in the phone to my PC it is recognized as an MTP device. A tool like Eraser http://eraser.heidi.ie/ is not able to choose this destination to erase. I am also not sure how the partitions are handled in Android. Is it enough to erase securely the complete internal storage after resetting, wiping, reflashing the phone or are there still areas of interesting data around other partitions?!

Would be glad to get some advice

This is my suggestion:

1. wipe your phone and storage, data...
2. flash new ROM
3. adb shell: dd if=/dev/urandom of=/sdcard/junkfile (http://zackeryfretty.com/posts/secure-erasing-android-devices-guide-for-the-super-paranoid-seller)
4. adb shell: dd if=/dev/urandom of=/data/junkfile (http://zackeryfretty.com/posts/secure-erasing-android-devices-guide-for-the-super-paranoid-seller)

Any other suggestions?