Inspect your valve seat to make sure there isn't a tear where it affixes to the little clip. If there is, replace the seat. Also, it is not necessary to push down firmly on the end of the BeerGun™ when filling a bottle. This is the most common source of the seat slipping off of the clip. Lastly, you can "glue" the seat in place with a dab of silicone sealant. However, this precludes you from removing it for sanitizing.