I remember several years ago seeing a commercial for a major lure manufacturer that featured a guy sitting next to a large tank of water. The man would toss a lure tied to a stick in the tank and watch to see how the lure would behave when retrieved through the water he would then make adjustments to the lure until it would swim through the the water to his satisfaction. Fly tiers can use the same idea to test and make modifications to their flies as the lure manufacturer did to test lures.

  First off you don't need anything as elaborate as a tank the size of a water trough, in most cases if you are testing dry flies, wet flies, or nymphs a soup bowl or cup will do, preferably your tank should be clear so you can see your fly from all sides. For flies or bugs that require action a shallow cake pan or tub will probably give you enough room to test your creations in. However the ideal test tank is an 5 or 10 gallon aquarium minus the fish. The aquarium has enough room to move flies in and the depth gives a good indication of how fast a fly will sink or how a dry fly looks from the fish’s perspective. The whole idea is to be able examine and scrutinize your flies and bugs to see how they look in the water, see how they might look to the fish, and to evaluate and test the properties of materials that make up the pattern.

  Tank testing can be a real advantage to those of us that are having trouble getting the proportions of our dry flies correct. On a dry fly with good proportions the tail and hackle should support the hook so that it appears to barely break the surface tension of the water. Test dry flies in different sizes and patterns to see which ones ride the highest then set the ones that ride on the water the best aside to use as models when tying a batch of the same pattern.

  Wet flies and nymphs can also be tested as well. Hold the flies under water with a pair of tweezers or mount the fly to some thing that doesn't float and place it in a container with clear sides. Pay attention to see if the materials in the fly, particularly dubbing, change color (most materials appear darker when they are wet)
and to see how materials like soft hackle and marabou move. You can also see what effect teasing dubbing has on the appearance of the fly as well as how much flash or how many air bubbles the fly traps. This is also a good time to see how sinking agents or the addition of weight affect the fly.

  For tiers of bass flies tank testing is a great way to see how a fly behaves in the water and to refine the choice of materials used in construction. This is the time to find out how materials behave when wet and importantly how much water affects the weight of the fly. Some natural materials like rabbit fur will weigh more and will become more difficult to cast when they are wet than synthetic materials that don't absorb water. It is also a good way to develop techniques for fishing these flies. You can see what happens when you attempt to vary retrieve speeds or what kind of action can be imparted to the fly and as in wet flies see the affect of adding or removing weight.

  Some of the best lessons can be learned by trial and error and fly tying shouldn't be any different. Testing your flies in water under more controlled and easily observed conditions gives you knowledge and insight about flies and bugs that is difficult or impossible to get while you are actually fishing. By tank test your flies before you use them in your fishing you'll be helping yourself become a better tier and hopefully a better and more successful angler.