Update: I got air mattress nozzle adapters for my pump and it sealed perfectly! Apparently this is just a larger version of the more standard pinch valve on smaller inflatables.
Original post: I was setting up an inflatable pooland all the other adapters were the standard size pinch valve and I was doing alright until I came across this big guy. It's similar in design but the diameter is almost an inch wide! I thought maybe they wanted me to fill up the pool's walls with water but there's no threading on this valve. What type of air hose adapter would fit this big guy?
Sometimes these larger valves are for quickly deflating but can also be used for inflation too. Many of them are “two stage” where the top part of the cap is a regular sized valve and the bottom is large like in your picture. If you only have a regular inflator, then you can try to stick it in there and seal around the rest of the opening with your hand. If you wanted some weight in there, I don’t see why you couldn’t fill it up with water at least to the valve and finish it with air.
I actually did that and it was hell and a half to fill it up and even worse to empty it all out. I checked for an opening on the valve's cap but there's nothing to fit in there, infortunately