I’ve been using a muslin/“nut milk” bag for years. I’ll grind a pound of coffee and let it steep for a couple of days in roughly a gallon of water, then pour it into a dispenser that I can leave in the refrigerator.

I’m no coffee snob but to me the flavor keeps extremely well.

The only thing I found is that even the finest mesh bag leaves a considerable amount of grit so I pour that through a paper filter. Hard to beat fantastic coffee at the turn of a spigot.

The first recommendation I give to people that want to get into brewing better tasting coffee is to get a burr grinder, even a handheld one will do just fine. With a burr grinder you just get a more consistent grind which helps reduce the fines thereby reducing the bitterness.

I second this, but do get one with a metal burr like a Timemore, and not the oft-recommended Hario Skerton, which has a ceramic burr.

The manual grinding experience with a metal burr grinder is so much better.

I use my Baratza for my day to day coffee, but that was not a cheap upgrade.