I think we need an image Izzy. I too have a chimney which I use for plants. I drop a plant pot into it. It did take me a while to find one that fit.

If its how I imagine it you could fill up to the level of the first hole, put your plant in and fill up to the next one etc, rather like you rill a wire hanging basket..
Its a good idea to sink a tube or something down the middle so that when you water some of it goes lower down rather than just wetting the top bit.