Nice work on the acrylic! Looks sharp
(in the good way). Have you water tested yet?
I must say, your tank is really looking like it's on the road to recovery - looks pretty nice.
For the threaded nipple problem, believe it or not, that's a pretty common problem with sprinkler systems as well
. Have you considered using a riser-removal tool? I had to hunt to find a pic of one:
http://reticonline.com.au/cw135/inde...roducts_id=587
You can usually pick these up from your local home improvement store for about $5.... should do the trick for you I think.
Keep up the good work!