1/4 cup of household bleach for each 15 gallons of water.
Empty the fresh water tank.
Add about half a tank of fresh water via the city water connection.
Disconnect the fresh water hose at the trailer, and pour the measured bleach into the hose.
Connect the hose and let another gallon or so of water run in.
Drive a few blocks, let the water slosh around.
Open each tap and let it run awhile. Flush the toilet.
Empty the fresh water tank.
Flush city water through the each faucet till the bleach odor is gone.