Platypus HyperFlow Bite Valve Cap leaks?

I bought the cap and it leaks when any pressure is on the bag. I see it’s a taper fit to the bottle any suggestions to correct it? Anyone else have similar problem? thanks

Guess I’ll go for an o-ring and try that

Mine has been trouble free. I used to use it primarily in the winter for skiing and hiking. Would fill it with Finlandia and Gatorade.

I’ll try an o-ring and see don’t want to break the sellers chops on ebay for what it cost it’s not his doing.

I got a refund from the seller

put in two o-rings and it still leaks. I would have paid seller if it worked. Oh well still bothers me I cant fix it.