joint on pvc gutters

these are joined by a strip of pvc inside and outside the two gutters where they abut
the pvc strip inside the gutter is raised above the inside lower level of the gutter, trapping water in each gutter length, the height of the pvc strip, creating a breeding area for mosquitoes
one way to get around this would be to drill small holes in each section, to relieve the the pools of trapped water
another may be to not use the inside pvc strip, but to join the gutter sections with the outer pvc strip only and use pvc cement for strength and leakproof connection
anyone had experience with this and have a solution?
also, how much can gutter slant ruels be ignored to greatly increase the water flow?
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