How often you need to dump depends on several things
Shower (RV or Park) if you use your own you need to dump more often
Toilet: Sea-Land type (Gravity) or Macerator (more "Thirsty")
Dishes.. Paper or plastic or china, the latter two need washing.
Size of tank, Mine are 36 Gallons times 3 tanks (one just for the shower and bathroom sink)
When Wife was alive we usually dumped 2x a week She used a maceration toilet, Me the Sea-Land. (Bath and a half model) We use park showers.
However we once went 8 days.. On the road, very "Conserving" of water (Wife also used Sea-Land, it uses far less water)
Now living alone.. I dump normally once a week, save last week was too Q@#W$REQ@#W$R Hot out so I went 2 weeks. Dumped about an hour ago
I now use the shower but am on a full hookup so the drain hose for it is water trapped and the valve left open.