Thanks for the replys.....my belly is enclosed....I crawled underneath on both sides...never saw any sort of valve other than the low point drains....the owners manual is pitiful....doesn't show anything....
The enclosed underbelly is standard. There should be three tubes sticking out, in front of the tires. The two on the door side are the low point drains for the plumbing system (should be a sticker on the outside wall near them). The single tube on the off-door side, just behind the sewer connection, is the water tank drain. Each tube should have a small brass fitting on the end, which is a valve. The "handle" is tiny, but it is a valve.
I don't think HL has changed to a screw-off cap, like some other brands have, but if there is a big white cap on the end of the tube, then unscrew it and the water will flow.
About the only thing the owner's manual is good for is starting campfires. So generic that all a RV company has to do is change the cover and they can all use the same one. It was no different with our TT.