Sorry, I didn't respond to your question about how I got my valve off. It did screw directly into the fiberglass tank. The three pipes into the valve were connected by unions so I simply unscrewed the unions. When I couldn't get the valve to budge I hit one of the pipes with my hand so hard the pipe broke off at the valve. I was able to remove the screw in connection and repair that mistake. I tried with all my might to unscrew the valve and couldn't get it to budge. Next, I took a hammer and tapped the valve in a couple of places where I thought it might help to loosen it. I put a piece of cloth between the valve and the hammer. I thought I might break the valve, but luckily it held. After I had tapped it several times in two places, I tried again to unscrew it and it did unscrew. I removed the sand with a tool that hooks to the garden hose that my pool store loaned me. I checked internal piping and laterals and I put in 350 lbs of new sand. When I attempted to put the multiport valve in with teflon tape and teflon paste and hooked it up it was leaking pretty bad. I pulled it out again and tried more tape and paste, but this time it blew out when I turned the system on. I took the valve out again and noticed that some of the threads on the valve were actually broken and the threads in the fiberglass were kind of mushy. I tried to seal it with plumbers goop, but that didn't work. I used marine grade epoxy from Lowes and so far it has been holding at least three days and looks like it will continue to hold.