If you try to use ordinary speed bits or masonry bits, they are very likely to break. You need a 'spear-point' or 'spade' drill. From another post: I have some considerable experience in drilling hard materials, with 30 yrs in the glazing contracting business (glass company). We regularly drill all sizes of holes in glass/mirrors, granite (shower door installations) and other vitrified materials (the objects people bring to us to drill holes in). Ease of drilling varies with the hardness of the material, of course, but terra-cotta containers are not hard at all. Most containers you'll encounter can best be drilled with a "spear-point" drill. I'll link you to a picture from one of our suppliers. The drill is also called a '3-point' or 'spade' drill. Highly vitreous containers (glass, or glass-like - ceramic - clay fired at high temperatures) may even require a diamond impregnated "core drill", but it's uncommon to find containers like this. These drills can be found at big box home improvement stores. They should be cooled with water or a 50/50 mix of water/antifreeze as you drill. An excellent strategy is to immerse the container upside down in a tub and add enough water to just cover the drilling surface as you drill. Rotating the drill clockwise at a slight angle while drilling will greatly increase ease of operation. Alternately (I use this method), fill a squeeze container (contact lens solution bottle is stellar) with water or 50/50 water/antifreeze & squirt it at the drill/material interface as you drill. If you can't find the drill you need, you can contact me off forum & I'll be glad to help you. See a picture of what the drill looks like below. They are made of carbide and designed to drill very hard materials. Here is a link that might be useful: Click me and I'll show you one of the drills Al's talking about.

What some people do when planting regular plants in a large or deep container is to fill it with some stuff that isn't needed for the container or plants, but it's just so they don't have to fill it with so much potting soil (and to keep it lighter than being filled all up with soil). I think the same ideas would be fine for your bog container, with the exception that you'll want to choose things which, when sitting in water all the time, won't have any adverse effects on the water or plants. Oh, and of course, I forgot that if it becomes a water container, then just water, with a certain amount of growing medium to allow the plants to grow in. Eg, an upside down planter, some plastic bottles, some sticks, plastic egg cartons, cut-up pieces of styrofoam, etc. Since your container is large-ish, then even 1-liter or 2-liter or 1-gallon containers might fit just fine in there.

Trust me, I do this all the time...start slowly from the outside until you barely poke through and finish it off from the inside. Forgot one of the most important parts of the drilling... keep the tip of the drill bit wet with water.. a puddle of water on top of the pot is must. It keeps the dust down, cools the bit and just makes for a better cleaner job! This post was edited by bikerdoc5968 on Tue, Jul 1, 14 at 14:04

Just a suggestion, someone might have a better one. You could try to find some sort of pan or tray such as this one, as long it's water resistant an sturdy http://www.newpig.com/pig/US/pig-utility-containment-tray-pak920?cm_cat=shop_by_product if you can't find out in the dimension of 4x3 than try two 2x3 pans(it would probably be better to get two since you will have 2 feet of heavy soil on top. Drill few drainage holes in the pans and put them upside down on the bottom of the planter. Place or glue on some window screen material on top of them so the soil won't drain inside the pan, just water. This way your soil will have some room for drain water to go instead of keeping it soggy.