Malon export vessel, eleventh gradient
You may also be looking for the larger Malon export vessel.

A Malon export vessel, eleventh gradient was a freighter-type vessel operated by the waste export industry of the Malon like most ship owned by the Malon it is classed as a garbage scow. They operated with a crew of nine.

The waste export vessel was designed for long range transport and dumping of theta radioactive antimatter waste and other mixed industrial byproducts produced by the Malon civilization. 

This gradient of vessel possessed three theta storage tanks, capable of carrying over ninety million isotons of contaminated waste. They were armed with spatial charge launchers and equipped with a tractor beam. ()

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Appearances
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Studio model
For this type of "Malon freighter," the revised final draft of the script described the following, "A large, bulky, cargo vessel designed to carry toxic waste." It also described that the freighter had "Several ports along the hull vent explosive bursts of toxic antimatter -- gas, debris, flotsam. The waste product of an advanced, spacefaring species."

Known then as the "toxic waste tanker" the design, finalized in , was a brainchild of Rick Sternbach who said, "I don't have a whole lot to say about the tanker, except that I wanted it to look massive, which the large spherical tanks seem to  accomplish. The spew nozzles are there, along with lots of supporting hardware like the carapace/spine, brackets, tubes, and so on. I  didn't develop a real style for the shapes and surfaces until the  later mega-tanker, which relied heavily, so to speak, on slightly  streamlined and repeating parts with a good old retro feel. Think steam and diesel locomotives."  Questioned about the  influences, Sternbach replied, "Except that mine aren't covered with yellow and black stripes. Also see Foss' Leviathan design for ALIEN. A similar approach on my part; completely unintentional."  The model was eventually built as a CGI model at Foundation Imaging by Brandon MacDougall, who commented about the model, "Toxic tanker was a lot of fun to build and texture and as always getting plans from Rick and the art department made the building a snap. Once built the ship was off to "Q" for the final steamer effects of green gas 'not shown in the rendering' back then it was over 1 hr for the gas to render one small frame." 

Being one of the more fleetingly-seen ships, McDougall out of courtesy re-rendered his model for Doug Drexler's blog. 
Starship classes