I plant tomatoes,peppers,eggplant,cucumbers,squash,bush beans and other vegetable in cattle feed tubs. They hold 25 gallons. I drill 4 holes in the bottom of each one. I use potting soil with nothing else in the bottom. I would take the drain plug out and drill a few more holes in the bottom of your stock tub.

How long have you had your tubs? Is is rusting where your holes are drilled?

Mine are made of black plastic. I guess you have metal livestock water troughs. I think I would try to use plastic instead of metal if I could.