I did the very same thing, washed my 6th gen in the washer. when i realized what i had done, i immediately put the ipod in a tub of rice. now it works, but only when it’s plugged in. I’m pretty sure it’s the battery that needs replacing. I’ve not replaced the battery as all of the things i need from ifixit are out of stock. If everything on the ipod works except that it won’t hold a charge and stay on unless plugged in, then it’s most likely the battery and replacing it will probably fix the problem.