Go to amazon and order this umbrella stand:
Go to Costco and buy the Tommy Bahama beach umbrella. They usually have them for $19.99 to $24.99. If you don't have a Costco nearby then you can also order the one below from Amazon but the price is higher.
Once you have the umbrella stand, pull the filler plug and coat with a good quality sealant such as marine 5200 and replace the plug sealing the chamber airtight.
Cut the bottom off the piece that holds the umbrella shaft..from now on we will call that the collar. You can use a serrated kitchen knife to do this, the chop saw was probably over kill.
Go to the hardware store and get a 1" coupling, a 1" Tee, and a piece of 1" THIN WALL 200psi PVC pipe (((SCHEDULE 40 IS TOO THICK AND WILL NOT WORK!!!!!!))) This should all cost you about 5 bucks. Cut the 1" PVC pipe making a 3 foot long and a 2 foot section. Glue the pieces together with the coupling and glue the Tee on the end of the 2 foot piece.
Slide the pipe through the base with the Tee on the bottom. Slide the collar you cut the bottom off of down the pipe from the top until it hits the coupling. CAREFULLY heat the collar with a hair dryer or heat gun JUST until you can slide it over the coupling stopping when bottom of collar and coupling are flush. It should be very tight. If your coupling is loose you will have to glue the collar to it. Slide collar nut over pole and insert collar properly into base and tighten nut carefully.
Get an old sock and fill with 7 lbs of rock, lead weights, sand, whatever then tie the sock through the Tee.
You could also use a plastic covered dumbbell or concrete filled bar weight...sandbag...ect.
Drop the umbrella in the pipe and relax!!
Now that you have everything you've ever wanted in a floating pool umbrella here's more!! To complete the experience you HAVE to have somewhere to put your drink right?
Just thought of one more thing...If you would like more stability you can simply cut a piece of the Large size pool noodle 2 feet long and then slice it down the side and slip it on the bottom pipe. You will of course need to add more weight to compensate but you will end of with a more stable platform..