My old sump used 7" socks and I ended up making my own filter cup for it. The actual hole for the filter sock on my sump was exactly 7". A 6" schedule 40 pvc coupling is 7.25". My list of parts was the 6" coupling,, a piece of 6" sch 40 pipe (mine was 8-9" long), and a flush mount end cap for the piece of pipe. First step was cutting down the coupling to be used as the lip. I cut mine to 1/2" as my pipe went through the sump cover into the sock to begin with. If it goes to its own chamber and then overflows into the sock, you will want to make the cut area of the coupling considerably thinner. I glued the coupling cutoff to the 6" pipe, then took my router and cut slots for water to pass through (drill and drill bit would work as well), and installed the push in end cap. I think total cost was about 25 bucks to build it. The only piece I glued was the coupling cutoff. It worked very well and I could even throw a sock into if needed (little cramped at the top) when I stirred things up moving something around or cleaning the sand.
The above mentioned is about to be used on my newest tank's sump, but in a dual 4" setup. I am going with my version of the Triton Method, but want to be able to use socks or media if needed. Both of them have me at 15 bucks total cost of parts, as I still have pvc cement and primer this time lol. If going with this idea, just be sure to measure the hole for the filter sock. Make sure it is smaller then the coupling. If your water dumps directly into the sock the lip can be thicker. If it overflows into the sock, it needs to be thinner.
