I do not know the size, but Briggs makes two of their own drains. One is the plastic quick drain with the replaceable hose. The other is a permanent option which I had used on my 18hp Briggs. I have included a link to that hose. You can ask Briggs directly and they can tell you if it will fit up.
The best-value buy; Briggs and Stratton 1723165SM Hose-Oil Drain – Replace cracked drain hoses easily. Flexible yet durable construction. Shop now!
www.briggsstrattonstore.com