most newbies freak out about the black tank, when it's the gray tank you should be more concerned about.
for one person, it would take weeks to fill the black tank, so don't worry about a 3 day trip. just dump it before you leave, either at the full hookups connection or at the dump station.
we use Odorlos for our black tank. simply dump it down into the black tank, through the toilet.
the gray tank will fill much faster and you could fill it in the 3 days if you use the sinks or shower a lot.
personally, i would use this trip to learn about your trailer's systems. so use the toilet, sinks and shower and learn about monitoring them and emptying them.
