First thing I did on both of my TTs before even using them was to replace the stock cap with a cap with a hose fitting. I don't ever use a hose on it, but I can remove the hose cap first slowly to verify there is nothing in the drain before pulling the main cap off. If it starts leaking I can then put the hose under the hose connection to catch what's in the there before I remove the main cap. Has worked great so far!
2006 Jay Flight 29BHS
1999 F350, XLT, 4x4, 6.8L V10, AT, CC, LB