Maybe new atf,but I wouldn't run used in it.You'd be better off running it on urine,than on used,for the same reasons..shrapnal will wreak havoc on everything dear to you.I've got a waste oil heater in my home shop,and run,new oil,new atf,diesel,or home heating oil in it.I don't even run old stuff in that,and it's actually made specifically for it.When I used to run used oils in it of any kind,I was taking it apart very week for cleaning,and filters.Now,I do it once a year,at the end of each season,and the parts are pretty clean when I open it up.