First off, it is recommended that you replace your pump with one that is comparable in HP and GPH(Gallons Per Hour). We only carry the round basin covers that will cover an 18" round basin. The check valve can be installed either at the base of the pump or just above the basin cover. Installing above the basin cover will make it a little easier to disconnect your discharge for any service. Also keep in mind that you should drill a 3/16" hole in your discharge pipe just above the discharge base to help prevent any air lock.