Newer model dual flush toilets have come a long way in terms of design. Steeper bowl sides and improved flow designs have eliminated many of the past bowl-streaking transgressions that plagued the genre. However there is one kind of dual flush toilet that never streaks more than a non-dual flush version. What I'm referring to here is a dual flush retrofit kit.

Dual flush retrofit kits convert your existing toilet tank into a dual flush system. The idea behind a dual flush system in the first place is to utilize a full flush for solid waste and a reduced flush for liquid waste. Now, if you have a low-flow toilet already, your full flush is using about 1.6 gallons per flush, or 6 liters. I don't hear many people complaining about low flow toilet streaking. If your low-flow toilet was converted to a dual flush system using a retrofit kit, guess how many gallons of water you will be using for solid waste? That's right, the same 1.6 gallons. It's only when using a half flush, 1 gallon only, that the water flow changes at all. This holds true for any size tank, the reduced flush will always be 1 gallon and the full tank is the full flush.

So what we've learned here, is that while buying a new dual flush toilet, depending on the model and manufacturer, might leave you with a streaky bowl, converting your existing toilet to a dual flush system never will. If it does, you already had a streaky bowl problem to begin with and it might be time to break out the rubber gloves.