Honda Pioneer 1000 2017 Owner's Manual page 84

To access the under seat storage, remove the front seat (page 139).
Cargo should not exceed:
UNDER SEAT
under seat storage
The under seat storage is equipped with a drain plug. When driving
through water, the plug should be installed to help prevent water
from entering through the bottom of the storage area.
The under seat storage is not waterproof. Do not place items that
could be damaged by water in the under seat storage.
If water does accumulate, the drain plug can be removed to allow
for water removal. (Include picture of drain plug)
Be careful not to flood this area when washing your vehicle.