Looking at a 2003 Roo 21 for sale online, it looks like yours has a u-dinette and no slideout.
Have you looked inside the dinette cabinets?
Did you find the drain tube station under the trailer?
I know that some older Roos had the drain valves inside, while newer ones have a threaded cap on the drain tubes underneath.
Unfortunately, not aware of any members here that have that year/model.
Dan-Retired California Firefighter/EMT
and Zoe the Wonder Dog(R.I.P.)
2016 PrimeTime TracerAIR 255, pushing a 2014 Ford F150 SCREW XTR 4x4 3.5 Ecoboost w/Max Tow Package