When it comes to burying a 25 foot flagpole, the depth that you bury it will depend on a few factors. The first factor is what type of ground you are dealing with. If you have soft soil, then you won't have to bury the flagpole as deep as you would if you were dealing with harder soil. The second factor is how windy it is in your area. If it's very windy, then you'll want to bury the flagpole deeper so that it doesn't get blown over. The third factor is how big the flag is that you're flying on the flagpole. If it's a large flag, then you'll need to bury the flagpole deeper so that it can support the weight of theflag.
Generally speaking, though, most people who are burying a 25 foot flagpole will dig a hole that is about 4 feet deep. This should be enough to keep the flagpole securely in place, even in windy conditions and with a large flag attached.