I unclogged my standpipe.
I bought some 8 foot pieces of PVC (1/4 inch), put screw together joints on them, screwed together about 70 feet of it and took a cobweb brush (plastic stiff bristles) and Gorrilla taped it to the end to make one l-o-n-g plunger. I pushed it up through the valve end until I ran into some mud and debris. After some vigourous brushing, the clog broke free and water is running out the top of the standpipe again. The PVC was flexible enough to curve through the valves, but stiff enough to put some ooomph behind. Not sure how the mud got in there because there feels like a screen is over the pond side inflow pipe. Maybe it built up over time.
Thanks for all the advice.
