Get yourself a bulb type siphon from Wally World, just a few bucks. Remove the plastic plug from the water heater. Insert the small section of the hose into the hole and let the curved hose angle down into the water heater. Put your thumb over the other end of the hose. Squeeze the bulb a few times. If there is any water, release your thumb from the end of the hose and let it flow.
On my TT if I open the low point drains (I have three) and remove the plug from the water heater not all water drains out. The openings in the water heater for the lines and the plug do not sit on the bottom of the tank but a few inches above trapping the water as it falls below the openings. When I use the siphon it seems like maybe a half gallon or so of water still comes out.
Camping World sells a water heater saver thing.. It's a wand you hook up a garden hose, stick it in the bung and it flushes out the tank (Kind of like the black tank flusher but everything comes out the same hole it goes in)
Try one
Also pop the lever on the TPR valve to let air enter at the top of the tank
Nothin adds excitment like something that is none of your business John is Near Kenwood TS-2000 housed in a 2005 Damon Intruder 377