This may sound strange but, it works really well. Rocks. Mix some seafoam with a couple gallons of gas, add to tank along with a couple handfuls of small rocks. Dime to fifty cent size. Shake tank vigorously. If possible, put them in the back of a pickup truck and go down the bumpiest road you can find. Remove rocks and flush tank.
:smile15:
Strapped to a four wheeler across the pasture would work too.