First trip out a great sucess 2 questions please

Hi,

Traveled about 50 miles from home first trip.  We wanted to be safe and close if something went wrong.

My wife Melissa and I (Doug) were so worried that we would not enjoy the camper enough to offset the rather large expense of getting the camper.  Boy were we wrong!!!! We had a great time.  We towed our 3023 with our GM Silhouette minivan with the towing package.  The vehicle and camper performed great!!  We had no power problems, and best of all we traveled with another friend that had a trail lite 22ft camper and they got 11 miles per gallon (Bravada) we got 23mpg.  Thanks to those who put all the good advise about the toilet,  our dealer had the toilet charged to the full mark.  Thanks to those who had the correct advise we were able to set proper and use the toilet for three days and still have room to spare.

Sorry to ramble on, we are just so happy!  As for our questions, first the grey water tank.  The brochure states that there is a 30 gallon capacity.  Is this correct?  Day one my wife and I did dishes she washed her hair, minor water useage and from 12:00pm to 7:00 pm the holding tank gauge read full.
I emptied and it did not take very long,  after one small bath for our 2yr old son and one meals dishes it read 2/3 full and washing evening dishes it read full again, could my gauge be broken?  We did not dump again, but continued to use for 2 showers, dishes and one more bath, never backed up.  Help please, what should I check?

Question #2:  We have the back up electric water heater, If you turn that on do you turn the inside water heater switch off the book is unclear,  I thought I still heard the gas heater lighting during the night and running???

Thanks for any help anyone can provide!!

Doug and Melissa