Step 3: Boil to Soften the Meat and to Remove Additional Fat.
Fill the pot with enough water to cover the pieces. Bring to a boil, then continue boiling for 15 minutes. After this, dump the first boil, and rinse the meat to further remove fat and dirt that hasn't (yet) been cleaned off. After you rinse the meat, fill the pot to with enough water to cover the ox tail, and boil it for a second time. (If the fat content of this stew is not an issue to you, skip the second boil.)
If you have a second 8 quart pot handy, bust it out. If not, keep the meat in a collander or strainer and clean your pot to remove the fat (and dirt) you've boiled out.