Plastic Drum Standpipe Washtank Plans

By Rick Da Tech


Plastic Drum Washtank PlansA favorite biodiesel wash tank for many is the plastic drum. If you choose the 'natural' color, you will be able to see the biodiesel and water through the drum. Poly drums are easy to find and dirt cheap.

Shown here is a plastic drum sitting on top of a wooden stand. The drains need to be attached to the stand to prevent them from loosening when the valves are operated. This stand has wheels but that is not required.

The typical plastic drum will have two 2" bungs. One bung will be a course threaded butress thread. The other will be standard 2"npt pipe threads. There are two styles of bungs, those with internal thread or "adapter bungs", and those without internal threads. Most drum will have the adapter bungs with 3/4" female pipe threads in them, but if they don't, you will need to aquire some for this washtank.

The internal or female threads are sealed at the bottom and have to be cut out to make them useful. Use a knife to cut them out without cutting into the threads. be sure to bevel the cut to allow the pipes to screw into and through the bung.

The special part that makes a standpipe possible in plastic drums is the standpipe itself. The standpipe is an 8" black pipe nipple that has had the threads cut in them three inches long. It screws into a bung containing 3/4" female threads. Most of the hardware stores have pipe thread cutting machines and can cut the threads long if you ask them. Often it will be at no extra charge. It is hard on the dies to make the extra long cuts, so there might also be an additional charge.

Stand Pipe

If you screw the bung all the way to the end of the threads it will seal better. It helps to have a vise to tighten up the elbow before installing in the drum since you will not be able to tighten things up in the drum without deforming the bung and causing leaks.

biodiesel washtank Stand Pipe

Once everything the elbow tight, your ready to mock up your standpipe in your drum for the final fitting. Nothing short of a bung wrench will get the bung tight enough to prevent leaks. I've made a custom bung wrench that will slip around the standpipe and still tighten the bung properly. I've only shown the standpipe, but you will be mocking up both the standpipe drain and the low drain bungs at the same time.

tightening up the standpipeModified Bung Wrench

pb19Once the bung is tight, then rotate the pipe in the bung so that it points 90 degrees away from the other bung, with both bungs pointing in the same direction, and tighten the lock nut. Remove the bung from the drum without disturbing the pipe alignment relative to the bung. Once it is out, fill the inside of the bung with silicone and reinstall it back in the drum a final time. Make sure the pipe is oil free before applying the silicone or it will not stick.

Now is the time to add the 12" pipe nipples and mount the drum in a stand. The stand is important to the overall construction because you will secure the ends of the 12" nipples to give enough support to the pipes to prevent them from moving when the valves are operated. The method you use will depend on the type of stand you use. When using a wooden stand, the most secure method is to have them pass through holes in a 2x4. This calls for positioning the drum in the stand, marking the location where the pipes would pass through the wood, then drilling holes in the wood. Once the tank is mounted in the stand and the ends of the 12" nipples are secured, than add the ball valves.  Allow a week for the silicone to cure before putting any liquids in the tank.

biodiesel standpipe drawing

Item Qty Description
A 1 Fine thread bung reducer
B 1 Coarse thread bung reducer
C 1 3/4" standpipe
D 2 3/4" black elbow
E 1 3/4" x 4" pipe nipple
F 2 3/4" x 12" pipe nipple
G 2 3/4" brass ball valves
H 2 3/4" PVC insert adapters


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