Have your tank inspected by a septic tank professional every three to five years - more frequently if your family uses a lot of water and/or a garbage disposer. You can reduce the strain on your septic system by using less water and staggering showers, clothes washing, bathing and other heavy usage.
When using dowels, select a size half the thickness of the wood being joined. For example, for 3/4-in. stock, consider 3/8-in. dowels.; for 7/8-in. stock use 7/16-in. dowels. The length inserted should generally be three times its thickness. Thus, a 3/8-in. dowel should be about 2-1/2 in. long to penetrate into each member 1-1/4 in.