This is a chain link fence post cut about 3 foot long, bolt is welded onto washer, washer welded to one end of post. Painted all and drilled a hole thru the post and umbrella post for a hinch pin.
6' patio umbrella will fit inside. Very stable and solid when put into threaded seat base. Maybe this will give another idea also.
Here are a few pics of the setup I made that works for my wife and I can use it as well on the front if I want . I don't have much in it as all but the two joints were in my pvc scrap and the umbrella is one my wife used when our kids were young and played soccer.
May all the fish tales you catch be longer than the ones you tell !