I suppose it depends on if you're trying to race liquids through your system, or trying to build up your hydration level, those two ideas require different approaches.
I for example drink a glass of milk and sometimes also a glass of water right before bed. This allows me to get to bed and be in a dry diaper for around two hours before I start wetting it, but having gotten well-hydrated, I usually wake up in a pretty soaked diaper by morning, having wet 4-6 times on the average. I wore a Kiddo diaper to bed last night, which although it does pretty good to protect against leaks, is limited somewhat by only having two tapes. So as long as I don't flood, it usually can go pretty high capacity without leaking, as was the case last night. It's also slightly more gentle on my skin, only sleeping in a significantly wet diaper for 3-4 hours instead of 6-7.
The other option is "diuretics", things that lower your hydration. There isn't just one, there's a lot of different chemicals that are diuretics to some degree or other, and you'll probably hear others mention a few here. Caffeine and Alcohol are the most common two. Since both are consumed alongside water which helps hydrate you, but that's not going to stick around for very long. If I drank that before bed, I'd probably end up doing most of my wetting within the first 3 hours, which isn't what I'm trying to accomplish. (the caffeine also makes it harder to get good sleep) I prefer to enjoy my diaper throughout the night with smaller wettings every time I wake up.
On the other hand, if you're just going to be wearing for a few hours and want to wet heavily a few times in the brief time you're diapered before you change out, caffeine or alcohol is probably the way to go.