When the word that begins a dependent clause and several of those clauses are linked together with and, there is NO comma before the and even when the word that is missing
and is "understood."
NOTE: The word that can be left out of a clause when it has no other function in the
clause except to introduce the clause.
...I know that he was there and that he was willing to help.
...I know that he was there and he was willing to help.
...I know he was there and he was willing to help.
...I know he was there and that he was willing to help.
However, if that is not introducing a dependent clause but is part of an independent
clause, there should be a comma.
...He had called in sick, and that was unacceptable.
...She sent a nasty memo, and that was causing a lot of discontent.
Happy punctuating!
Margie