After reading a few stories about lost drain caps, I made my own solution. It's kind of a redundant system, as I installed a 1/2" pvc ball valve to replace cap, but also used cap to keep debris out of drain. Parts include...cap, trimmer line, stainless steel rivet (with center removed) and food grade silicone caulk. Drilled cap, inserted rivet, threaded line, melted and flared end to hold in rivet, sealed with caulk. Made loop with zip ties and heatshrink.