A tall tale.
There once was several wealthy merchants in the Koronus Expanse, though their names have be lost the winds of time. It is known it was 5 who signed the agreement, and that with their combined wealth they would hold the greatest monopoly over the Expanse. This agreement was called the Black Concordant. For many years they reigned, underbidding, out buying and selling all their opponents. As with all greedy entrepreneurs, this wasn't enough for some. And so with great zealous the weakest of the Black Concordant yearned to be more powerful than the rest. It just so happened that all of them invested in the construction of a ship that personified their power, greed, lust, and secret desires. A Universe Mass Conveyor named "The Concupiscence of Desire" was built that embodies everything anyone ever craved. All 5 members of the Black Concordant would meet once a year on this ship to splurge on their gluttony while sailing in the void. This is where Rescule 'Pfishor' Illuis made his move. Hiring a handful of very skilled assassins, they were able to introduce a toxin into the food supply of the Atropaths which ensured that no communication with the outside world was enabled. From here the assassins planted explosives on the Navigator Spire that connected to the rest of the ship, which caused the Spire to be jettisoned into space, while simultaneously damaging the Warp Navigation Device. Pfishor and the assassins then escaped the blind and mute ship in a shuttle, enroute to a location where another vessel was going to pick them up. Unknown to them, the ship picking them up was slowed down due to an ambush by Eldar. When the ship finally arrived at the point a month late, all but one assassin was alive. And he only survived because he was eating the dead. No one knows where The Concupiscence of Desire went. Some say Dark Eldar found it, while others whisper the ship wondered into a star.
A rare few RT's have heard faint rumors though. A vast ship floats quiet in the void. It's corridors are lined in jewels and gems, with servitors serving spoiled food on golden trays. Many rooms line it's rusty halls, that sense your deepest desires and tempt you with it so that you will forever stay in their embrace. And vaults that contain valuables that rival the richest of RT's are guarded by crazed men that laugh and smile as they slit your throat. The last rumor some pub drinkers have coined the phrase as "The Pfishor's Debate."