I know it is not the ideal material, but the current holding tank
is metal (steel or aluminum, I didn't look to closely), but it seems fairly new, with strong welds, etc, on the outside anyway. I noticed that it only has one air vent, and I have read about experts advocating 2 vents. I assume that I could buy another vent fitting, drill a 2nd vent hole (filling with water ./ talking top hose off, to avoid an explosion!!)
Do you think that adding a 2nd vent would be worth the trouble?