I would strongly, STRONGLY, suggest a rubber bulb, not the soft squishy silicone that's more commonly found. Unfortunately I bought mine over 20 years ago and its holding up perfectly, otherwise I'd share a link to buy it with you. I suggest rubber bulb because its harder to squeeze, its not that soft, and because of this, you are sort of forced to squeeze really slowly, which you want to do so you don't shoot water into your colon, you don't want to do that, it takes time for it to come out and during intense bottom play, you wind up with a mess later on. Just want to flush the rectum out.
Aneros makes a bulb, I have it (although it is good, I prefer my rubber OG bulb), and its designed to prevent backflow in case water gets sucked back into the bulb while inserted, and it is designed to be squeezed quite hard to get the water to come out of it, to fill up the rectum slowly.
good luck in your quest!