Going to the toilet too frequently on the run leg can be easily avoided. Know your sweat rate per hour at race effort for cold and hot days, and be flexible when the temperature changes during your Ironman. You need to have a well-rehearsed hydration strategy so you don’t drink too much volume during the bike and run – drink smaller amounts every 10-15mins rather than larger amounts every 20-30mins.
It’s okay to consume slightly less than your sweat rate per hour, however you want to avoid a loss of more than 1% body weight during the Ironman. Studies have shown that consuming 1.5-4mg/lb of body weight can improve performance, any more has not proven beneficial and can end up being a diuretic. You may have a different sensitivity to caffeine during endurance events, which can cause you frequent loo stops. You just need to establish what you can tolerate.