I have a valve on the top of mine. What I do is put my hops in a muslin sack that has a weight in it, at the start of the ferment after pitching the yeast I put the hops in the head space tied with some cord that then goes under the lid and tied on the outside. When I’m ready to dry hop the valve is closed for a while to get a bit of pressure, then loosen one of the clamps and drop the cord so the hops enter the beer, after a while open the valve again. When dry hopping is over I do the reverse, close the valve wait a bit, release the clamp a bit and then raise the bag into the head space, then open the valve. The valve has a tube into starsan similar to the above.