Medtronic make (or maybe used to make) the "minimed sportguard"; currently about $80 on amazon.com
The case is claimed to be "waterproof". I couldn't find what that meant, but while searching I did discover that Medtronic have pretty much denied that the Paradigm pump is waterproof in any meaningful; they apparently say it shouldn't be used when swimming or taking a shower!
The sportguard case itself can't be found on Medtronic's own online store, so quite probably it is no more waterproof than their previous attempts.
There's a lot of information here:
That discusses the AquaPac 158 case; this is the one they explicitly sell as an insulin pump case:
It's using a clamp style closure on the tube, which means you don't have to detach the tube to get the pump inside, however the case is less waterproof than the original (now denied) Medtronic claim for the Paradigm. (It can only last for 5 seconds if under 3ft of water pressure, so the clamp has no pressure resistance.)
The tests Imperial performed (reported on the forum page and on the AquaPac page) also included the 550. That case showed a better result (92% flow) and I think the clasp is identical to the smaller case, so you would probably be able to get the pump in without disconnecting. The case rating, however, still doesn't allow for any water pressure so you can't use it while snorkeling and even swimming is a little risky (don't get the case more than 3ft deep!) AquaPac have this to say:
"Waterproofness Warning!: This case features our 'TC' Aquaclip which makes the case waterproof to IPX7. Temporary immersion is fine, but not continuous immersion."
Notice that in both cases the Imperial tests showed no flow reduction for high flow rates; the reduction was only detectable over 2 units. My assumption is that this is a feature of the pump they used (a Roche), however the reduction over an hour (1.16U worst case) is more than enough to block my own basal over that time (0.5U).
The issue with pumps is that the ones designed to work with substantial pressure increases - 40% for the Ping, 80% for the Omnipod - need to have no substantial air pockets in front of the plunger. That's because an air pocket will be compressed, to 1/1.8 (55%) of its volume in the Omnipod case, and that compression will replace the basal insulin flow. So my basal will be stopped for a whole hour if I take my Omnipod to 25ft and it has a 0.9U volume bubble of air in front of the plunger.
(Incidentally, if you do the PADI open water course you get taught all the pressure stuff, and there's a question on it in the written exam. I thought that one was a give-away, but that's just me.)
Anyway, a bubble of that volume (0.009ml) has a diameter of 1.3mm (that's not part of the OW course :-). That's a pretty big bubble; visual examination of the bubbles in my Omnipod reservoirs suggest that they don't exceed 0.5mm, which is about 0.0005ml/0.05U and way below the amount necessary to make a significant change to my basal.
Any pump that doesn't have to deal with water pressure, however, has far looser constraints. Pretty much the only issue is that the pump has to deal with the pressure change in pressurized aircraft; this corresponds to at most 8,000ft of elevation, pressure reduction to 75% of sea level, and happens over a period of maybe 30 minutes. Atmospheric changes due to weather are much slower and don't typically exceed this anyway.
My suspicion is that the Roche pump which showed 42% flow rate just happened to have a larger air bubble as a result of less careful priming.
If you believe me then simply releasing the clamp on the case will release the insulin; the case doesn't actually cancel your basal, it just delays it.
All the same, what I don't like about either of those cases is that they really aren't pressure proof and that they compress the tube linearly. Inserting the tube through a grommet would work far better, and this is the technique used on (hard) camera cases to allow moving components to penetrate the case so the camera buttons can be operated.
I can't see any problem feeding the tube through a case with a grommet. Unfortunately I also can't find any cases that use this arrangement. I had thought iPod/MP3 cases did this, but the ones I've been finding have built-in, sealed, headphone jacks (the AquaPac 518 for example) not grommets that accommodate a moveable cylinder like the hard camera cases.
None of this is very helpful, unless you were considering changing to a different pump manufacturer, but I think that things will get better in the future as pump manufacturers compete over the very large market amongst active diabetics for waterproof pumps.