If you are using a slow cooker to make your bolognese sauce, there are a few tips you can follow to prevent it from becoming watery. First, make sure to brown the meat and vegetables before adding them to the slow cooker. This will help release excess moisture and add more flavor to the sauce. Additionally, you can also add a small amount of tomato paste or cornstarch slurry (made with equal parts cornstarch and water) to thicken the sauce. Make sure to stir well before serving. Finally, leaving the lid slightly ajar during the last hour of cooking can also help evaporate excess liquid and thicken the sauce.