What is this big black worm ?

I just cleaned out my 20long that has been sitting for months. No fish or heat. Just dirty water,plants and a piece of wood.
Found this black worm thing. Swims like a fish. 2 inches long, gets shorter. The last fish in there were all born in my parasite
free tanks. I was going to use this tank, now I don't know if it should be sterilized or burned. Gross !

PIC?

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sounds like a leech, they sometimes come in with live food type worms....but kill it with FIRE!!!

I took some pics, but don't know how to load them. They didn't look like anything that I've looked at. Thinking it's a leech of some kind.

It's most likely a leech that usually comes with live black worms. If that's the case, then yeah. Leech. Now I don't think these types suck blood, but they do eat the black worms. If you see any, take em out and smoosh em. My fish don't eat them, so they are useless to me

I've never bought blackworms. This thing was in an old tank. I gave away all the baby bristle nosed that were in it months ago. Tank has just been sitting there as it was when the fish left. Same old water,no food,half dead plants, old piece old wood.I want to reuse the tank to house poppa BN temporarily. I cleaned the tank out completely.