In an interview from this article by HP Newquist, originally published in GUITAR Magazine (September 1995):

What about effects?

Diambag Darrell: Honestly, I go straight through my stack with just a couple of rack things. Live I just have my soundman out front. He does my delays – his choice of the delays, I don’t’ care, just put the fucking echo on there when it’s needed. We do have the delays all time out. He also does some Harmonizer stuff to double the runs on some of the songs off of Cowboys From Hell so that it sounds like we have two guitars playing. Through my rack I have an MXR flanger/doubler. It’s not really an effect because it’s on all the time, and my tech and I work tight on that sound."

In Premier Guitar's Rig Rundown, you can see MXR Flanger Doubler in his rack at 1:51

This effects unit was sold on Billy Corgan’s official Reverb.com shop.

Used for Timbaland's vocals on Justin Timberlake's "SexyBack", as stated by mix engineer Jimmy Douglass in this July 2007 Sound on Sound interview.

Lead vocals: Universal Audio 1176, MXR flanger, Izotope *Trash*

"The signal chain for Justin's vocals was an Audio-Technica 4060 mic, into a Presonus ADL600 mic pre, and then a Universal Audio 1176 limiter. I normally use the U87 for recording vocals, but I was curious about the AT and I had both mics in front of Justin. The effects I used on his vocals seemed to work better with the AT. I used the U87 on Timbaland's vocals and went straight into the desk. I like using the Neve VR mic pre. It's a little crunchy, it's not quite the 1072 or 1073, but it works.

"Justin then said 'Man, can you put some effect on the vocal? Something crazy, like a distorted kind of thing?' So I put the Trash plug-in on [Izotope's distortion, filter, delay and amplifier modelling plug-in]. I just happened to have it. To give you my exact settings would be silly. But I'll give you one clue: it wasn't something that I worked really hard to get. Just by using the plug-in the setting almost came up.

"The Trash plug-in wasn't the only thing I used on the lead vocals. I also had an outboard MXR flanger on it. Plus there was an outboard compressor, the Urei 1176. I used the same three effects on Timbaland's vocals, just less than on Justin's. But you can hear the flanger and compressor acting in the spaces, like just before Justin sings 'dirty baby'. There's no hiding it, and it creates a whole other dimension of sound."

Used for the vocals on "SexyBack", as stated by mix engineer Jimmy Douglass in this July 2007 Sound on Sound interview.

Lead vocals: Universal Audio 1176, MXR flanger, Izotope *Trash*

"The signal chain for Justin's vocals was an Audio-Technica 4060 mic, into a Presonus ADL600 mic pre, and then a Universal Audio 1176 limiter. I normally use the U87 for recording vocals, but I was curious about the AT and I had both mics in front of Justin. The effects I used on his vocals seemed to work better with the AT. I used the U87 on Timbaland's vocals and went straight into the desk. I like using the Neve VR mic pre. It's a little crunchy, it's not quite the 1072 or 1073, but it works.

"Justin then said 'Man, can you put some effect on the vocal? Something crazy, like a distorted kind of thing?' So I put the Trash plug-in on [Izotope's distortion, filter, delay and amplifier modelling plug-in]. I just happened to have it. To give you my exact settings would be silly. But I'll give you one clue: it wasn't something that I worked really hard to get. Just by using the plug-in the setting almost came up.

"The Trash plug-in wasn't the only thing I used on the lead vocals. I also had an outboard MXR flanger on it. Plus there was an outboard compressor, the Urei 1176. I used the same three effects on Timbaland's vocals, just less than on Justin's. But you can hear the flanger and compressor acting in the spaces, like just before Justin sings 'dirty baby'. There's no hiding it, and it creates a whole other dimension of sound."

Backing vocals: MXR flanger, Digidesign Impact, Sound Toys Filter Freak, Celemony Melodyne, Waves Q10, Metaflanger and Renaissance Reverb, Pultec EQ

"The backing vocals are all Justin. I'd say it's about 12 tracks, three-part harmony. I'm sure I used the MXR flanger on this as well, and also the Impact plug-in, which is supposed to simulate the SSL board compressor. I wanted to really hit it hard, with an attack-y kind of sound that releases really quickly. I also used the Filter Freak plug-in, which is great, and Melodyne, Metaflanger, the Waves Q10 EQ, the Pultec EQP1A and the Rverb [Renaissance Reverb] plug-ins. Rverb is not a great reverb, but I like it, because it's low-grade. The weird backing vox effects are a combination of things, and I have no idea how I did what."

At 6:40 in this video with Future Music Magazine you can see the MXR Flanger directly above one of Ulrich's Publison DHM 89 B2's.

Shatterproof Drum Programming [Simmons SDS5, Roland TR808], Sequencer [Sequencer Programming: Arp Odyssey, Arp Sequencer, Moog Modular], Electronics [Treatments: Ibanez AD80 Delay, EMT Plat Reverb, Mutron BiPhase] – Benge Vocals [MXR Flanger Doubler, Yamaha Rev1 Delay], Synthesizer [Synthesizers: ARP Odyssey, ARP Omni, Korg Monopoly] – John Foxx

Okay, back to the rack. Next, there’s the MXR Flanger/ Doubler. Notice that in the top photo, which is from later than the lower one, I’ve covered up both MXR rackmount units with black tape. I did this because people were always sniffing around, trying to figure out how I got my sound – and that’s, of course, ironic, because I 100% stole the Flanger/ Doubler idea from Darryl from Pantera.

According to the "equipment list" found on Church Studios, owned by Epworth, one of the things listed are MXR Flanger/Doublers.

You can see it in the rack @ 3:30 mark as well as his explanation & thoughts on it.

In this video you can see Philippe Zdar showing an MXR Flanger Doubler

can be seen at 02:06