You can purchase degreasing agents specifically for tanning such as Super Solvent ( a Bruce Rittel product) however, Dawn dishwashing detergent as well as Simple Green are very effective & available most anywhere. Dawn now makes Dawn Ultra, which is a concentrated formula... they claim 2 times the grease cleaning power, just bought some to try. Just be sure to wear gloves. these detergents are harsh on hands/ skin . Any smaller skins are good to practice on, even squirrels. you can also cut deer hides into smaller pieces for practice tanning. I use dawn & simple Green for degreasing oily fish skins like Lake trout & Salmon also.