Our spring project is going to be a bog at the top of our stream and I think I've settled on a stock tank. I'm not sure how to create the outflow from the bog though. What stops the pea gravel exiting with the water?We have a few preforms and stock tanks that drain into the next part of the pond loop. For our outs we just drilled a one inch or two inch hole, stuck a piece of one or two inch pvc in the hole, gooped it up with pl roofing goop, let it dry, done. It has been that way for 4 years now.