I never go to PO, I just use paypal shipping.
That said, wrap each bottle in bubble wrap. Tape. Then, place those into a ziplock bag, and you can tape the top of that, too.
No way these are leaking.
The reason they ask: If you read the USPS regs on liquids, you will see they are only concerned about leakage and/or huge drums of stuff. Or that they are flammable and/or Glass and other breakable containers. This is because these things go on airplanes, and/or they don't want postal workers getting soaked with leaking things. People mail shampoos, conditioners, etc. all the time and they don't package correctly, so this makes
sense.
See section 3.4:
DMM 601 Mailability
So you can just say shampoo or food flavorings if you're concerned about it, and let them know it is properly packaged.