What Brand AND Model????
ONLY Suburban uses an 'anode rod' ----NOT Atwood
To drain/flush
Turn water supply OFF
Relieve system pressure by opening a Faucet Hot/Cold Sides-----leave it open
Remove drain plug ---water WILL flow out emptying the WH Tank
I turn water supply back on ---turn faucet off and let water Blast out WH TANK drain hole. CAUTION: Stand Back as it will BLAST out
Turn water supply back off....install drain plug (new anode rod if Suburban) and open faucet hotside to bleed air out of plumbing system and allow WH Tank to fill.
Water flows/no air from faucet-----done
Nosey FLAME on water heater
Atwood has an adjustable air shutter
Suburban no air shutter so could be dirty orifice, dirty burner tube etc
WHAT water heater do you have????