Thank you all for the great info and thank you Freeheeler for your checking. They are coming to get my tractor tomorrow AM to install the backhoe. I had a long talk with the salesman about the loaded tires....He has sold many and all with loaded tires....he sez, "hell" I'll call the manufacturer and get the skinny for you.....
called me back and said no problem as the makers of the unit say it is plenty strong enuf ….can't remember the brand of unit, but it is what Kubota sells here. He sez the manual says to remove weights from tires because of some humbug like not having the bucket on loader or something like that...snow job, I think...ha ha.
Guess the water stays in. I could get it out, but would worry about the rims rusting...no way to get all the water out unless the wheel was broken down and dried out.
I will keep up my investigation, but for now...the weighted tires will stay.