What does the CDL manual warn can happen if a tank vehicle driver steers quickly while braking?

49 CFR 383.119(i) (operating practices and procedures not otherwise specified); AAMVA CDL Manual §8.3.2, p.8-8-2

A loaded tanker already has a high center of gravity, and surging liquid adds extra sideways force on top of that. Combine that with a sharp steering input while braking, and the vehicle can tip before the driver even realizes how close to the edge of control they are.