We are very concerned about anything that could become a containment in our product and work hard to avoid any contamination for our customers. Adding tape or a clip lock will lead to a potential contaminant – especially if it fell off and got into the bag during transport. As a result, we are against using anything that could come loose. We tested tying the bottom bag, but the knot / lump caused the double stacking of the bag to lean too much which could cause a tip over during transport. We are currently plastic wrapping the bags to keep them upright to avoid this problem.