Why do a dip?
I think a good bath,in some good quality flea shampoo,and then once dry,give a dose of a good topical treatment of flea meds.
There are many out there,ask your vet what they sell,or even go with a natural holistic type. I think most pet stores sell them.
I don't think the dog needs dipping,just monthly maintenance.Although I will add,since you know he has fleas,then they are in your home as well.
It's scary how many flea eggs hatch a day.So a good cleaning with very hot water to all bedding,curtains etc,and also a deep steam clean of your carpets.You have to stop the cycle of fleas in your home.