Another RTBS owner.
RTBS are aggressive fish and if you don't plan for it they can raise merry hell in a community aquarium. However, with careful planning and setup you can minimize their aggression and integrate them into a community aquarium. First off, minimum tank size for a RTBS is 30 gallons, and that's if you don't plan on having much else in the tank. If you want them in a good community you need to go larger. I have a 48 gallon corner tank that works out magnificently as it has good bottom area and is rather tall. A 55 would work nicely but expect one end to be the RTBS's domain.
So, how to control your RTBS? First off the fish is primarily aggressive in regards to its territory. So the key to controlling your RTBS's aggression is by planning out its territory. First off, your RTBS is going to want a cave/cover. This will be it's home. Like Pasfur said a flower pot on it's side would work great for this or an artificial cave. I built my RTBS a cave from slate. I'd highly recommend putting this cave to one side of the tank. Secondly, the RTBS's territory is largely based off what it can see from it's home. The less of a view they have the less territory they claim as their own. So I strongly recommend heavily planting your tank be it real or fake. This will limit the RTBS's territory and give the other residents of the tank somewhere to get away from your bruiser. Finally, and this is the worst part, believe me I know, is to add your RTBS to your tank last and as young as you can get them. When added to an established tank and when young your RTBS is far less likely to claim the whole thing as their own domain. They'll pick out a smaller territory they feel they can defend and stick to it.
A few other things, first off RTBS's are bottom feeders. You'll find yours spends most of their time on the bottom. Secondly they are quite a bit like cories in that they are scavengers. Good quality sinking foods supplemented with the occasional algea wafer will be good staples for your RTBS. Just like a cory, a RTBS couldn't bite another fish if it wanted to, their mouth is oriented all wrong. My RTBS will occasionally chase off another fish that strays to close to her territory but she doesn't bite. The RTBS gets a bad reputation because just like a cory they are the first on the scene to start eating a carcass. A lot of people see their "shark" eating a dead fish and assume the RTBS is an active predator. They're not, they're just opportunistic scavengers. You can tell if your RTBS is male or female by looking at the belly. If its as black as the rest of them its a male. If its gray it's a female.
They're magnificent fish, I love my Mekong to death and dote on her like no other fish. She's a touch on the pudgy side from the regular diet of shrimp pellets, algae wafers, and frozen food she gets. She occasionally feels the need to put the other fish in their place but most of the time she's perfectly well behaved. Oddly enough the only fish in the tank she ignores are the cories. They can wander into her cave and poke about and she does nothing. Go figure.