I will try the single drain for now, it's all I got. I want to get a bigger sump and switch to a Reef Sump someday, so the good news is that I can just buy new bulkheads and refit the HOB overflow. I know the sump is designed for 125 to 150 gallon tanks. So It's not what I would want forever, but it will work for the initial set up.
I want buy a drilled tank as my next tank, but that will require a better job, one I hope to have one day. I got this tank because it was used and cheap, so I can get my Yellow Tang, Yellow Eye tang, and the Luna Wrasse out of the 55.
It's a 120 LONG (5 foot long), and I might one day just upgrade to a bigger canister filter, as this will only be a FOWLR tank forever, and not a reef. Just not have a sump at all because the HOB overflows are not that great!