Having googled the image I can't imagine any plant surviving in!

Creeping jenny - the golden leaved variety is nice, it is more or less evergreen ( Lysimachia nummularia 'Aurea' ) , you can get bog primulas, there is Japanese Horsetail (Equisetum japonicum) and a smaller version (Equisetum scirpoides)
There is also the corkscrew rush which is evergreen (Juncus Effusus Spiralis), the Red Stemmed Parrots Feather - (Myriophyllum Brasiliensis), For a colourful plant you could consider Houttuynia cordata 'Chameleon' (Chameleon plant) .

You could also experiment with a miniature hosta such as hosta blue mouse ears as I have grown the hosta "patriot" as a pond marginal all year round for the last two years and it is doing well . Growing it in water keeps the snails and slugs off as they can't swim!

There are numerous water plants - if you google pond marginals you will get a better idea of just how many there are!

You are lucky, I've always wanted one of those!!! agree with weedfingers lots of choice there.

Plants that like to grow in wet conditions do so where the water is moving. Any plant in your pig feeder is going to be sitting in a sump of stagnant water which will rise higher and higher, especially in winter. This means that the plant will be deprived of oxygen and will eventually die. You could try filling it with water and simply putting aquatic plants into.

you could get a punch or a drill and make drainage holes which in turn would give you a lot more choice however if you go to a pond specialist they sell marginal plants that would do fine in water .

I just wanted to add that of the plant I mentioned, I have the yellow leaved creeping jenny, the normal sized Japanese horsetail, the Chameleon plant and the hosta " patriot" and hosta "halycon" living with their roots in stagnant water as marginal water plants. I don't have any form of water flow in my pond and they are all thriving. The pond is healthy and has frogs and tadpoles living in it.

Weedfingers the water in your pond wont be stagnant and neither will the water in the soil around the pond, it will evaporate and soak away into the surrounding soil. You don't need to have a flow of water through the pond - we don't but the water is changing all the time, either you top it up somehow or you get enough rain to keep it topped up. In the pig feeder the water really doesn't have anywhere to go.

stagnant water is like you would find in an old tire once you introduce plant life etc and rain its not stagnent or there would be a lot of stagnant small lakes and big ponds.

Thanks all- I will drill holes in I think and then I will have a greater choice :)

Have fun Claireliz

good luck