aggie, you really don't need a pump for only four fish.
Are you planning water lilys, plants, etc?
Unless you want some sort of fountain, waterfall, etc I would just use a inexpensive air pump for a little circulation.
Do you have a well?

Seal the hole with 3M� Marine Adhesive/Sealant 5200. You can get it in a small tube at the hardware store.

Corrie

Hi aggierose,

I'm no expert on pumps and filters, but I'll share with you what I know.
I have 2 in-ground 300 gallon Rubbermaid stocktanks. One is a lotus bog and the other is a little pond. I can't remember the exact size of my pump, but I think its 450gph. I don't have a pump in my lotus bog.
In the pond, I have a little waterfall and it works great.
My pump sits inside a filter box at the bottom of the stocktank, with a tube running up and out through the waterfall rocks.
If you have a pump outside the stocktank, yes, there will need to be a tube that goes from the stocktank to the pump, and then another one that goes back out to the stocktank. You could put that tube to a small fountain, so to aerate the water.

Just be aware of how much soil you will need to move, in order for the stocktank to fit. Its alot more than you think!
About the stocktank plug. What I did was to put some plumbers tape around the screw and screw it it tight. Then I took some caulk and went around the plug, just to be on the safe side.
You will definitely need a pump and filter with those fish, since they make alot of ammonia.
Plant lots of plants in your stocktank.......some oxygenators on the bottom, something like a small water lily to cover the surface and then 1 or 2 plants on milk crates that give some height (like an iris, pickerill rush, etc.)
The milk crates work well because they give the fish places to hide from things like raccoons, heron.
Hopefully someone more knowledgeable will give you advice about an outside pump and filter.
Good luck.

Rally, I don't need a pump? I guess that's good news, except I really would like a fountain so I will need a pump for that at least. I won't have a waterfall.

Aggierose,
May I ask why you want to use a stock tank. You are planning to put it in the ground so why not just put a EDPM rubber liner in. It is going to be far easier to install, last about 10 times longer, can be made into any shape and cheaper.
Mike

Mike, I was just discussing this with my husband. He asked why I wasn't going to just use a liner and I couldn't give him an answer. What are the advantages of using a stock tank, if any? If I just use a liner, do I just dig a hole, spread sand and then lay the liner? I assume there is more to it than that, but maybe not. This probably sounds a little odd, but one thing that has always bugged me about pond liners are the creases that are visible. Is there a way to get rid of them?

Corrie, I forgot to tell you that I will definitely be putting plants in the pond.

Aggierose,
Yes it is that simple. You can use sand or what ever else you might have for under the liner. Then it just becomes what you want to do to hid the top of the liner. As far as the folds in the liner. Yes they can be gotten rid of but it takes someone who is very good at seaming liner. But in most cases after the pond is about six months old they just disappear on their own. They are still there but you don't see them any longer. There are no advantages to using a stock tank in the ground that I know of.
Mike

I really think you need a pump.
I think the benefits of a stocktank are that you can't tear it. I plan on having mine last forever. But I think the sides of a liner are easier to hide.

A stock tank can warp and crack, especially if it is not absolutely straight. It is very hard to repair a cracked tank.

I would go with a submerged pump. You will need some type of filtration and moving water is the easiest way to keep the water oxygenated and won't smell bad. Dallas/Ft.Worth is hot and warm, still water loses oxygen fast.

The only real problem you may have with a poly tank in ground is getting it level and making sure its supported well. The bottom of the hole will need to be very flat and have a little bit of sand put in it (to aid you in leveling) or the bottom of your tank can sag as it settles from the water weight. If you take your time and do it right it should be fine if that is what you want to do for a pond. You could probably do a liner pond for what you will spend on that size of poly tank.

I would get a pump. You don't need anything real big, just enough to get some circulation and run a fountain.