Why does the breaker keep tripping on a circuit with two rooms' lights and a sewer pump?
Sewer pump should be hooked up to GFCI.  So that is the first step - change out the outlet to a GFCI.  The reason this will help you is first it is code in some places and second if the pump is the culprit then it will pop the GFCI outlet.

Also is this a 20 or 15 amp circuit.  Some sewer pumps are rated for 20 amps and above.  I actually have almost the exact same situation in my basement.  And the pump does flip the breaker every once in a while.  You are lucky to have lights on them.  We had a couple outlets and one powered our deep freezer.  

So get a GFCI.  You could have a short - so look at the connections for everything.  Then the last thing is look at the panel.  If it is 15 Amp you might need to take the pump off the circuit and run a 20 amp line for it with 12 gauge wire...