As these seem to be a recirculating type of tank, how do you fill them? Portable bilge over the side to fill?
Garden hose attached to the faucet at home works pretty well. A bilge pump on a hose works also. Use a cigarette lighter plug for power.
Do you fill with brown, muddy river water or fill at home with clean water and if so what about chemicals in a public water supply?
Depends on the time of year. If the tap water temperature is fairly close or warmer than the river/lake water, I use tap water. If it's cooler by more than 10 degrees (as it will be in the heat of summer), I use a 50/50 mix of tap water and lake/river water.
If you use water from a municipal system, you'll need to pick up a bottle of "Tap Water Conditioner" at the nearest PetsMart, PetCo, etc. and follow the directions. A bottle lasts a good long time.
River water can be used any time you want - the filtration system will clean it up in an hour or so; you'll have to replace the filter element more frequently until it clears, but that's no big deal.
How do you empty them without pulling a plug and having all the nasty water go into the bilge? Pump it out too?
Creek Bank tanks come with an adapter that you can plug into the pump outlet port. Add a length of hose and the tank can empty itself about 90%. The rest you'll have to take care of at home with a hose. Grayline doesn't have any kind of pump-out capability; use your portable bilge for that.
You'll also want to get a bag of Stock Salt from the nearest MFA or farm supply. Add about 1 cup per 15 or 20 gallons of water in your bait tank. Everybody lives longer and is happier that way.
In the heat of summer, you have to watch water temperature - more than 10 degree cooler in your bait tank will kill your shad in no time at all -- when they get all red-nosed and die, that's your clue that that water was too cold.
Spend the money on a good tank -- Creek Bank or Blue Water -- and you won't be disappointed. Buy a cheap tank and you'll get what you pay for...