Clay Sedimentation Tank – a DIY alternative

The standard, commercial sedimentation tank looks like the one on the right (this one, for example, is available from Bath Potters). It involves a plastic box with the water entering at one end and exiting the other. The box is divided into several compartments and the barriers between each compartment are at different heights. Once the first compartment fills with water, it overflows into the second compartment, and when that fills, it overflows into the next, etc. As clay material sinks in water (some quickly and some gradually), it will become sediment on the bottom of the compartments and the water that overflows to each compartment will be cleaner and cleaner.

I came up with a plan to do something similar with simple components. The first decision was to get a commercial kitchen pot cleaning sink for our pottery studio. This is made out of stainless steel and is very deep, and it comes with unusual, very tall, overflow plugs. I hadn’t seen these before but they worked out perfectly for what I needed to do.

I purchased two simple plastic boxes from Hobbycraft here in the UK, one about half the volume of the other, but both having the same height. The idea is that we wash and empty the clay into the smallest box, which then overflows into the bigger box, when then overflows into the sink. Notice, the tall stainless steel “plug” in the pot sink? This stops the water going down the plughole, so I can manage that (the plug has a hole in the top, but that’s quite high in the sink). However first, I need to explain how I manage a sensible overflow of water between the two boxes.

Before explaining how to manage the overflow, here’s a photo of the two plastic tubs just after I’d cleaned them out (it works out I need to do this every 4-6 months with our usage). It’s a messy business, cleaning out these tubs, but it would also be messy to clean out a commercial sedimentation tank. Now I’m going to show how I made the tubs overflow into each other in a controlled way.

In two corners of the smaller tub, I drilled a couple of holes like you can see here. The holes are quite high up. I want the small tub to fill quite high. The two corners that I drilled are the corners that are furthest away from the disturbance of the tap. It’s best if the water that starts passing through the drilled holes is as calm as possible, which means more of the clay will have had a chance to sink towards the bottom and hence be trapped in the tub and never make it to the drain.

Now, in one of the long sides of the larger tub, I drilled three holes. These holes have to be lower than the holes in the smaller tub, probably by at least 2-3 cms. This makes it possible for the water in the smaller tub to flow into the larger tub, and the three holes here in the larger tub allows the water to flow into the sink.

Here are the tubs put together in the pot sink. I’ve highlighted where the holes have been drilled. The two smaller circles show where the holes have been drilled in the smaller tub. The larger ellipse shows where the three holes are in the back of the larger tub.

The water originally gets disturbed by the tap or by washing in the smaller tub. Hopefully, a lot of the dirt will settle in this first tub and the water that overflows to the larger tub will be cleaner. Now, the holes in the larger tub are as far away as possible from where the water enters from the smaller tub, which should allow more dirt to settle in the second tub before overflowing to the sink.