I bought a PVC pipe cap at Lowes that fit the water tank drain perfectly. Sorry I can't remember the size, but can dig it out of the van if you are that interested. I also fabricated an elbow using regular garden hose parts that allows me to drain the water tank away from the van via a hose.This is handy when I drain the tank for storage and don't want to have a big puddle underfoot. 

-Tracey E