Take the Pavlovian approach and prior to the hot tub appointment put her on a regimen of several blowjobs per day. If she spits your spunk out or even complains about the taste, slap the hell out of her until she's crying and curled up in the fetal position. If she swallows without complaint, pat her on the head and say "Good girl!". She will be conditioned to love the taste of your cum in no time.