Welcome! Here are some tips for using this forum.
My W-M indirect storage tank Gold PLUS 60 doesn't have a drain for the inner (domestic water) tank. To periodically clean out sediment I hook up a low pressure air compressor to a hot water tap (sink faucet) open the cold water tap, and blow out the hot rusty water through the cold water faucet. Seems to work OK; am I missing anything?