Where does “Потопин” come from?

Потопин (Bulgarian) comes from Bulgarian потоп, from Proto-Slavic *potopъ — deluge, flood.

Ancestry of “Потопин”, step by step

Step	Language	Word	Meaning
1	Bulgarian	потоп	flood, deluge, inundation, flooding a very large and destructive flow or covering of land by water
2	Proto-Slavic	*potopъ	deluge, flood