Ok. I actually have worn quite a few revealing dresses when I was on the pump and here’s what I did:
I had the MM 722 (which is a bit clunky)
If strapless, but not backless, I wore a strapless bra with a plunging neckline. The lower the neckline on the bra, the better. Pushing those “girls” up would cause a gap where the pump would fit nice nestled in there. Then, the material on the dress would actually create a little pocket where the pump would not show through the fabric. So, meter in clip, meter face against cleavage, clip toward front of dress. If that makes sense. Face of meter against skin- so, basically clip it in the middle of the bra and have it facing backward.
If backless, and flimsy material, strap to thigh. You can either wear clipped inside thigh highs, I would put it toward the inner thigh area (where your legs naturally gap). Or, if you’re unsure about that, try wrapping a sock and/or strap around your thigh and clipping it to that. I wore a wicked flimsy dress to the casino once, it was backless and had a plunging neckline with no sleeves. I had no issues with my pump slipping and it didn’t show through the fabric either.
if backless, but has a bigger lower dress body, then you can clip to a pair of underwear and wear at the hip. I used to actually wear mine with a thong that had a large waistline. I used to call it my “sturdy underwear” because the band was thick, but it wasn’t too thick where the pump clip couldn’t go completely around the band. Also wear with the face of the pump against your skin, the clip toward the outside. This will keep the pump secure and will also reduce the amount of visibility on the outside of the dress.
At the VERY WORST, you can always go back to MDI for the night.