Personally there are two ways if I know I'm gonna have a long session or I really really don't want any accident.
1.
No spicy food,no raw food (well I love sushi) and no weird food. Only some well cooked chicken and vegetable one day before the party.
And the party day I won't eat anything at all but in the morning I'll drink a lot of water (for me it's cold or iced water becuz it triggered my GI tract reaction and I can go to toilet for a dump)
In the afternoon between 12:00-15:00 I'll take two pills of imodium (loperamide hydrochloride) usually it's not difficult to get from the pharmacy.And the function of it is to stop diarrhea. The side effect of it if you take a bit more is constipation which is what I want.And I usually start to clean myself two hours before the party or session and that's the time I take another two pills of imodium.
And of course, douche well !
2.
The second way is a bit more extreme. I used this when I really really really don't want any accident.
I stop eating for at least two to three days (but drink a lot of coke or redbull or drinks with high calories)
And then the party day, two imodium pills in the afternoon and another two before the party.
Usually this way I can be sure I'm clean for the whole night.
BTW, the longest time I stopped eating is 6 days.If you drink enough things it's actually not a big problem.
though I don't suggest this way.It's not for everyone.
I usually plan things ahead with my fuckbuddy for fisting so I can prepare myself well. If it's just a last minute random hook up then I won't do fisitng or huge dildos.
So for me I rarely have "accident"
Everyone's different and everyone's health condition is also different. I don't think there is a perfect method or perfect pill to achieve our goal to be clean always.