Steel Drum Biodiesel Wash Tank

The standpipe tank provides two drains at different heights. We make it out of a tight head or closed head drum and attach our plumbing to the bungs in the top of the drum. Then we flip it over so the plumbing is on the bottom and cut out what was the bottom for access to the wash tank.

Some have called it a poor man's cone bottom tank, but it is superior to the cone bottom tank. In fact, a common upgrade for cone bottom tanks is to add a second drain in standpipe tank fashion. The two different heights lets you get a cleaner drain than is possible with even a cone bottom tank. The lower drain lets you adjust the level of the water/biodiesel interface layer to just below the top of the upper drain. The upper drain then after purging will drain perfectly clean. One major advantage is that you can drain the biodiesel cleanly while leaving the wash water in the tank. This lets you reuse the wash water from the last wash again on the first wash of the next batch, thereby saving water.

The standpipe tank is not just a wash tank, it also makes an exelecent glycerin settling tank. When settling in a cone bottom tank, the glycerin will stick to the tank and slowly slide down the cone and contaminate the biodiesel with glycerin. You just don't get that kind of contamination with a standpipe settling tank. Another advantage of the standpipe tank over the cone bottom tank is that the typical cone bottom tank will NOT drain all of the liquid out. It will trap a little bit around the bulkhead.This causes havoc if the same tank is used for washing.

Standpipe tanks can be made out of almost any container. This one was made using an unlined drum. The best drum is one with a UN Food Grade linning. An unlined steel drum will develop a "chicken skin" if WVO is left in it. This does not seem to happen as fast with biodiesel. Biodiesel will also coat the drum protecting it from rust. The "chicken skin" does not form with the food grade linnings.

Item Qty Description A 2 ¾ hose barb to NPT adapter B 2 ¾” Ball Valves C 2 ¾” x 12” black pipe nipples D 2 ¾ black pipe elbows E 1 ¾” x 3” black pipe nipple F 1 ¾” x close black pipe nipple G 1 ¾” x 6” black pipe nipple H 1 2” x ¾” x ¾” Double sided bushing

The Double Sided Bushing

The traditional steel wash tank design requires that you crawl inside the drum to tighten the stand pipe. There is another way. The advancement is the double sided bushing. With it, you are able to get everything tight without having to put a wrench on anything inside the tank. The double sided bushing actually has three sets of threads. One set of 2" male threads on the outside that screw into the 2" bung and two sets of 3/4" threads that let you screw nipples into both sides of the bushing. With the traditional design, the stand pipe is held in place by only a couple of threads, with this design it is held in place by a full set of threads. That means a sturdier stand pipe.

First lay out the parts for the standpipe assembly.  You'll need a double sided bushing, a close nipple, an elbow, and an 8" nipple. With the exception of the double sided bushing, everything is readily available at the hardware store.

A 2" or 3" nipple with an elbow makes the lower drain. I used 12" nipples for the horizontal pipes to make sure the ball valves were both accessible from one side.

And a look inside the wash tank. It took me all of 15 minutes to assemble this wash tank, not including cutting out the bottom. A neat tip I learned from Dana S of Atlanta is that if you get your drum from a drum recycling company, they will have a fancy deheader that will cut the bottom out in no time flat, and you can take your drum home ready to assemble.