|Detective Phil Fish from Barney Miller. (Source: "'Tell Mike it was only Business': Abe Vigoda, who played Tessio in The Godfather films, dies at 94 in New Jersey"--Daily Mail).|
In any event, the issue is what to do with your firearm when you need to use the toilet (i.e., actually sitting down rather than using a urinal). As the TTAG article points out, the worst thing to do is put your gun on the toilet or on top of the toilet paper dispenser, a shelf or some other place where you might forget it. The author also notes a few solutions. He writes: "Some of you sought out that semi-private handicapped stall in the corner. Others wrapped the waistband of your undergarments around the butt of the pistol to keep Larry Craig-style looky-loos from noticing it." He also suggests that "[i]f concealment is truly a priority for you, and you believe that the lavatory is a high-risk zone for whatever reason, perhaps a smaller, .380 pistol carried in a pocket holster might be more appropriate."
What you do will likely depend a lot on what handgun you carry, how you carry it, how often you use the toilet and the type of restroom. Certainly, if you work in a place where the restroom is intended for use by one person at a time and you can lock the door, there is probably little risk of others seeing the firearm as you go about your business. On the other hand, public restrooms open to multiple users might present more of a risk of someone spying your firearm.
Frankly, to me, even the more public restrooms generally are not an issue so long as there is a private stall to use. I have learned that, when dropping my pants, to keep the waistband above my knees when sitting down. Typically, unless I'm using a pocket holster, I will have a holster at a 3 to 5 o'clock position (depending on the holster and what I'm carrying), so when I sit the handgun will be under my thigh and out of sight of someone that might try to peer through the cracks between the door and the wall panels. So long as I don't turn so my back is to the stall door, the gun is pretty much out of sight the whole time. Now, with a heavier handgun (such as a full size service pistol or revolver), you do need to be careful that your belt doesn't slip through the first loop or two and dump the belt and holster on the floor, but it is not a significant complication: just hold onto the end of the belt with your hand, or trap it between your elbow and thigh.
I haven't tried the trick of covering the handgun with the waistband of my undergarments, but I suppose that would be the best method if you carry the firearm on the front of your body (10 to 2 o'clock positions).
Mass Ayoob had noted in one of his writings that someone that has to use the toilet frequently may want to invest in a shoulder holster, a la the "Fish" character from the Barney Miller TV show (see photograph above).
In any event, don't remove the firearm from the holster and risk losing it, and don't let it hang down onto the floor where it can be seen under the stall door or wall.