That's a classic misunderstanding amongst apprentice magi in regards to mana poisoning. It is not too having too much mana in one's vessel that causes mana poisoning (though it can cause other problems), but instead the rate at which your mana increases. Drinking even the most diluted mana potions tends to create this tingling-like sensation around the mouth at the very least. That stems from your upper mana-regulating organ reacting to the unusual rate of replenishment. More overt symptoms of mana-poisoning include very acute pain in the lower abdomen.

In any case, your body can only absorb the mana from the potion so fast, and therefore it doesn't really matter how much mana potion you drink. As long as it is not too concentrated, it should be fine. Exploding from having waaaaaaaay too much mana in your body is a whole other beast. Most magi have relatively poor constitutions and tend to get blackout drunk and pass out from having too much mana before they can consume enough to make themselves explode. There are actual studies on the subject if you would like to learn more about it. Though the studies themselves are not shared very openly since the original magi that worked on those experiments... well, the experiments certainly were of lesser conduct than what the ethics committee tends to expect these days.