For the second application, regular car wash soap should be sufficient.
If you want something easier to help maintain/extend the life of the Liquid Wax, I would suggest taking a look at our Hybrid Wax as these two products were formulated to work together.
Since the Liquid Wax only needs to be applied 1-2 times a year, the Hybrid Wax is much faster/quicker to apply and can be used after every car wash or in between washes.
Hybrid Wax is also safe to apply to every surface on your vehicle.