I have to start this by thanking the people who've given me helpful advice. And to reply to this last lengthy post:
Okay... first... I'm not worried about overflowing the sump. If that was the impression people are getting, rest assured, that's not the problem. The problem is the stupid overflow box can't keep up with the return pump. Now that we got that out of the way...
The overflow box is a CPR model CS50. There are no ball valves on the inlet, and I don't know how anybody could get the idea from these posts that there is. As I said previously, I cleaned the inlet filter as best as possible and it has improved flow. The inlet hose has no obstructions. The return pump has a ball valve. It is cranked nearly shut. After cleaning inlet and filterbox I opened it some more but it still tries to overflow the tank. I do not plan on keeping this aquarium, it does not please me, and I don't want to sink money in a set up that I don't enjoy. I bought it mainly for the corals that came in it, I tried to buy only the livestock but the woman would only sell the whole set up. The sump is of unknown capacity, as I said in previous posts, the woman made it herself with lots of glass and silicone. Obviously, it being a standard 55, the sump is very small. Small enough to get in and out of a standard 55 stand. So I'd say less than ten gallons. And I'm not a complete newbie, I have been experienced with sumps and their principles, I have had several drilled tanks, and I do know better than to overfill the capacity for the event of electrical failure. The tank does hold siphon in case of shut off, but only with the use of the airlifter (I had a powerhead but it sucked so now it's got an old airlifter I had lying around). As far as I can read, the airlifter is the ONLY way to preserve siphon with a cpr overflow/prefilter box. I appreciate helpful posts, and I HAVE been the first to admit that I have NO experience with this HOB crap. I can't help but bristle a little though at the implication that I'm a complete idiot which I get from this last post. I don't think it's unreasonable to post to here asking for help from other people with more experience with certain types of filtration equipment, in the sake of saving my floor from innundation. I also don't feel that admitting to inexperience with one form is admitting to incompetence with all forms. Furthermore, I do think that experience doesn't make excuse for lack of tact. Often on this forum I see people get overly excited and jump down other people's throats for simple mistakes, sometimes with ample justification, but sometimes in no more sense than that of any mobbing. I don't necessarily think that PC here is trying to come off as arrogant and condescending, but none the less, as the person who's asking for assistance, I can say that's how it sounds to me. I'm willing to be wrong here too, maybe it's just been a long night of fiddling with this dang thing and getting no real results, and maybe I'm feeling a little like an idiot myself for the impulse buy.